diff --git a/cmd/lotus-sim/simulation/actor_iter.go b/cmd/lotus-sim/simulation/actor_iter.go
new file mode 100644
index 000000000..5df395e11
--- /dev/null
+++ b/cmd/lotus-sim/simulation/actor_iter.go
@@ -0,0 +1,38 @@
+package simulation
+
+import (
+	"math/rand"
+
+	"github.com/filecoin-project/go-address"
+)
+
+// actorIter is a simple persistent iterator that loops over a set of actors.
+type actorIter struct {
+	actors []address.Address
+	offset int
+}
+
+// shuffle randomly permutes the set of actors.
+func (p *actorIter) shuffle() {
+	rand.Shuffle(len(p.actors), func(i, j int) {
+		p.actors[i], p.actors[j] = p.actors[j], p.actors[i]
+	})
+}
+
+// next returns the next actor's address and advances the iterator.
+func (p *actorIter) next() address.Address {
+	next := p.actors[p.offset]
+	p.offset++
+	p.offset %= len(p.actors)
+	return next
+}
+
+// add adds a new actor to the iterator.
+func (p *actorIter) add(addr address.Address) {
+	p.actors = append(p.actors, addr)
+}
+
+// len returns the number of actors in the iterator.
+func (p *actorIter) len() int {
+	return len(p.actors)
+}
diff --git a/cmd/lotus-sim/simulation/block.go b/cmd/lotus-sim/simulation/block.go
new file mode 100644
index 000000000..677ba7a2f
--- /dev/null
+++ b/cmd/lotus-sim/simulation/block.go
@@ -0,0 +1,81 @@
+package simulation
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/binary"
+	"time"
+
+	"github.com/filecoin-project/lotus/build"
+	"github.com/filecoin-project/lotus/chain/types"
+	"golang.org/x/xerrors"
+)
+
+const beaconPrefix = "mockbeacon:"
+
+func (sim *Simulation) nextBeaconEntries() []types.BeaconEntry {
+	parentBeacons := sim.head.Blocks()[0].BeaconEntries
+	lastBeacon := parentBeacons[len(parentBeacons)-1]
+	beaconRound := lastBeacon.Round + 1
+
+	buf := make([]byte, len(beaconPrefix)+8)
+	copy(buf, beaconPrefix)
+	binary.BigEndian.PutUint64(buf[len(beaconPrefix):], beaconRound)
+	beaconRand := sha256.Sum256(buf)
+	return []types.BeaconEntry{{
+		Round: beaconRound,
+		Data:  beaconRand[:],
+	}}
+}
+
+func (sim *Simulation) nextTicket() *types.Ticket {
+	newProof := sha256.Sum256(sim.head.MinTicket().VRFProof)
+	return &types.Ticket{
+		VRFProof: newProof[:],
+	}
+}
+
+func (sim *Simulation) makeTipSet(ctx context.Context, messages []*types.Message) (*types.TipSet, error) {
+	parentTs := sim.head
+	parentState, parentRec, err := sim.sm.TipSetState(ctx, parentTs)
+	if err != nil {
+		return nil, xerrors.Errorf("failed to compute parent tipset: %w", err)
+	}
+	msgsCid, err := sim.storeMessages(ctx, messages)
+	if err != nil {
+		return nil, xerrors.Errorf("failed to store block messages: %w", err)
+	}
+
+	uts := parentTs.MinTimestamp() + build.BlockDelaySecs
+
+	blks := []*types.BlockHeader{{
+		Miner:                 parentTs.MinTicketBlock().Miner, // keep reusing the same miner.
+		Ticket:                sim.nextTicket(),
+		BeaconEntries:         sim.nextBeaconEntries(),
+		Parents:               parentTs.Cids(),
+		Height:                parentTs.Height() + 1,
+		ParentStateRoot:       parentState,
+		ParentMessageReceipts: parentRec,
+		Messages:              msgsCid,
+		ParentBaseFee:         baseFee,
+		Timestamp:             uts,
+		ElectionProof:         &types.ElectionProof{WinCount: 1},
+	}}
+	err = sim.Chainstore.PersistBlockHeaders(blks...)
+	if err != nil {
+		return nil, xerrors.Errorf("failed to persist block headers: %w", err)
+	}
+	newTipSet, err := types.NewTipSet(blks)
+	if err != nil {
+		return nil, xerrors.Errorf("failed to create new tipset: %w", err)
+	}
+	now := time.Now()
+	_, _, err = sim.sm.TipSetState(ctx, newTipSet)
+	if err != nil {
+		return nil, xerrors.Errorf("failed to compute new tipset: %w", err)
+	}
+	duration := time.Since(now)
+	log.Infow("computed tipset", "duration", duration, "height", newTipSet.Height())
+
+	return newTipSet, nil
+}
diff --git a/cmd/lotus-sim/simulation/commit_queue.go b/cmd/lotus-sim/simulation/commit_queue.go
index 957d301cf..63a478120 100644
--- a/cmd/lotus-sim/simulation/commit_queue.go
+++ b/cmd/lotus-sim/simulation/commit_queue.go
@@ -9,9 +9,13 @@ import (
 	"github.com/filecoin-project/lotus/chain/actors/policy"
 )
 
+// pendingCommitTracker tracks pending commits per-miner for a single epohc.
 type pendingCommitTracker map[address.Address]minerPendingCommits
+
+// minerPendingCommits tracks a miner's pending commits during a single epoch (grouped by seal proof type).
 type minerPendingCommits map[abi.RegisteredSealProof][]abi.SectorNumber
 
+// finish markes count sectors of the given proof type as "prove-committed".
 func (m minerPendingCommits) finish(proof abi.RegisteredSealProof, count int) {
 	snos := m[proof]
 	if len(snos) < count {
@@ -23,10 +27,12 @@ func (m minerPendingCommits) finish(proof abi.RegisteredSealProof, count int) {
 	}
 }
 
+// empty returns true if there are no pending commits.
 func (m minerPendingCommits) empty() bool {
 	return len(m) == 0
 }
 
+// count returns the number of pending commits.
 func (m minerPendingCommits) count() int {
 	count := 0
 	for _, snos := range m {
@@ -35,12 +41,17 @@ func (m minerPendingCommits) count() int {
 	return count
 }
 
+// commitQueue is used to track pending prove-commits.
+//
+// Miners are processed in round-robin where _all_ commits from a given miner are finished before
+// moving on to the next. This is designed to maximize batching.
 type commitQueue struct {
 	minerQueue []address.Address
 	queue      []pendingCommitTracker
 	offset     abi.ChainEpoch
 }
 
+// ready returns the number of prove-commits ready to be proven at the current epoch. Useful for logging.
 func (q *commitQueue) ready() int {
 	if len(q.queue) == 0 {
 		return 0
@@ -52,6 +63,9 @@ func (q *commitQueue) ready() int {
 	return count
 }
 
+// nextMiner returns the next miner to be proved and the set of pending prove commits for that
+// miner. When some number of sectors have successfully been proven, call "finish" so we don't try
+// to prove them again.
 func (q *commitQueue) nextMiner() (address.Address, minerPendingCommits, bool) {
 	if len(q.queue) == 0 {
 		return address.Undef, nil, false
@@ -72,6 +86,8 @@ func (q *commitQueue) nextMiner() (address.Address, minerPendingCommits, bool) {
 	return address.Undef, nil, false
 }
 
+// advanceEpoch will advance to the next epoch. If some sectors were left unproven in the current
+// epoch, they will be "prepended" into the next epochs sector set.
 func (q *commitQueue) advanceEpoch(epoch abi.ChainEpoch) {
 	if epoch < q.offset {
 		panic("cannot roll epoch backwards")
@@ -146,6 +162,7 @@ func (q *commitQueue) advanceEpoch(epoch abi.ChainEpoch) {
 	})
 }
 
+// enquueProveCommit enqueues prove-commit for the given pre-commit for the given miner.
 func (q *commitQueue) enqueueProveCommit(addr address.Address, preCommitEpoch abi.ChainEpoch, info miner.SectorPreCommitInfo) error {
 	// Compute the epoch at which we can start trying to commit.
 	preCommitDelay := policy.GetPreCommitChallengeDelay()
@@ -178,10 +195,3 @@ func (q *commitQueue) enqueueProveCommit(addr address.Address, preCommitEpoch ab
 	minerPending[info.SealProof] = append(minerPending[info.SealProof], info.SectorNumber)
 	return nil
 }
-
-func (q *commitQueue) head() pendingCommitTracker {
-	if len(q.queue) > 0 {
-		return q.queue[0]
-	}
-	return nil
-}
diff --git a/cmd/lotus-sim/simulation/messages.go b/cmd/lotus-sim/simulation/messages.go
index 76b100d75..3f1c55179 100644
--- a/cmd/lotus-sim/simulation/messages.go
+++ b/cmd/lotus-sim/simulation/messages.go
@@ -15,6 +15,7 @@ import (
 	"github.com/filecoin-project/lotus/chain/types"
 )
 
+// toArray converts the given set of CIDs to an AMT. This is usually used to pack messages into blocks.
 func toArray(store blockadt.Store, cids []cid.Cid) (cid.Cid, error) {
 	arr := blockadt.MakeEmptyArray(store)
 	for i, c := range cids {
@@ -26,6 +27,8 @@ func toArray(store blockadt.Store, cids []cid.Cid) (cid.Cid, error) {
 	return arr.Root()
 }
 
+// storeMessages packs a set of messages into a types.MsgMeta and returns the resulting CID. The
+// resulting CID is valid for the BlocKHeader's Messages field.
 func (nd *Node) storeMessages(ctx context.Context, messages []*types.Message) (cid.Cid, error) {
 	var blsMessages, sekpMessages []cid.Cid
 	fakeSig := make([]byte, 32)
diff --git a/cmd/lotus-sim/simulation/mock.go b/cmd/lotus-sim/simulation/mock.go
index e8a7b2d4a..b81ee8629 100644
--- a/cmd/lotus-sim/simulation/mock.go
+++ b/cmd/lotus-sim/simulation/mock.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/filecoin-project/go-address"
 	"github.com/filecoin-project/go-state-types/abi"
+	"github.com/filecoin-project/lotus/extern/sector-storage/ffiwrapper"
 
 	proof5 "github.com/filecoin-project/specs-actors/v5/actors/runtime/proof"
 )
@@ -21,74 +22,11 @@ const (
 	mockPoStProofPrefix          = "valid post proof:"
 )
 
-func mockSealProof(proofType abi.RegisteredSealProof, minerAddr address.Address) ([]byte, error) {
-	plen, err := proofType.ProofSize()
-	if err != nil {
-		return nil, err
-	}
-	proof := make([]byte, plen)
-	i := copy(proof, mockSealProofPrefix)
-	binary.BigEndian.PutUint64(proof[i:], uint64(proofType))
-	i += 8
-	i += copy(proof[i:], minerAddr.Bytes())
-	return proof, nil
-}
-
-func mockAggregateSealProof(proofType abi.RegisteredSealProof, minerAddr address.Address, count int) ([]byte, error) {
-	proof := make([]byte, aggProofLen(count))
-	i := copy(proof, mockAggregateSealProofPrefix)
-	binary.BigEndian.PutUint64(proof[i:], uint64(proofType))
-	i += 8
-	binary.BigEndian.PutUint64(proof[i:], uint64(count))
-	i += 8
-	i += copy(proof[i:], minerAddr.Bytes())
-
-	return proof, nil
-}
-
-func mockWpostProof(proofType abi.RegisteredPoStProof, minerAddr address.Address) ([]byte, error) {
-	plen, err := proofType.ProofSize()
-	if err != nil {
-		return nil, err
-	}
-	proof := make([]byte, plen)
-	i := copy(proof, mockPoStProofPrefix)
-	i += copy(proof[i:], minerAddr.Bytes())
-	return proof, nil
-}
-
-// TODO: dedup
-func aggProofLen(nproofs int) int {
-	switch {
-	case nproofs <= 8:
-		return 11220
-	case nproofs <= 16:
-		return 14196
-	case nproofs <= 32:
-		return 17172
-	case nproofs <= 64:
-		return 20148
-	case nproofs <= 128:
-		return 23124
-	case nproofs <= 256:
-		return 26100
-	case nproofs <= 512:
-		return 29076
-	case nproofs <= 1024:
-		return 32052
-	case nproofs <= 2048:
-		return 35028
-	case nproofs <= 4096:
-		return 38004
-	case nproofs <= 8192:
-		return 40980
-	default:
-		panic("too many proofs")
-	}
-}
-
+// mockVerifier is a simple mock for verifying "fake" proofs.
 type mockVerifier struct{}
 
+var _ ffiwrapper.Verifier = mockVerifier{}
+
 func (mockVerifier) VerifySeal(proof proof5.SealVerifyInfo) (bool, error) {
 	addr, err := address.NewIDAddress(uint64(proof.Miner))
 	if err != nil {
@@ -134,3 +72,74 @@ func (mockVerifier) VerifyWindowPoSt(ctx context.Context, info proof5.WindowPoSt
 func (mockVerifier) GenerateWinningPoStSectorChallenge(context.Context, abi.RegisteredPoStProof, abi.ActorID, abi.PoStRandomness, uint64) ([]uint64, error) {
 	panic("should not be called")
 }
+
+// mockSealProof generates a mock "seal" proof tied to the specified proof type and the given miner.
+func mockSealProof(proofType abi.RegisteredSealProof, minerAddr address.Address) ([]byte, error) {
+	plen, err := proofType.ProofSize()
+	if err != nil {
+		return nil, err
+	}
+	proof := make([]byte, plen)
+	i := copy(proof, mockSealProofPrefix)
+	binary.BigEndian.PutUint64(proof[i:], uint64(proofType))
+	i += 8
+	i += copy(proof[i:], minerAddr.Bytes())
+	return proof, nil
+}
+
+// mockAggregateSealProof generates a mock "seal" aggregate proof tied to the specified proof type,
+// the given miner, and the number of proven sectors.
+func mockAggregateSealProof(proofType abi.RegisteredSealProof, minerAddr address.Address, count int) ([]byte, error) {
+	proof := make([]byte, aggProofLen(count))
+	i := copy(proof, mockAggregateSealProofPrefix)
+	binary.BigEndian.PutUint64(proof[i:], uint64(proofType))
+	i += 8
+	binary.BigEndian.PutUint64(proof[i:], uint64(count))
+	i += 8
+	i += copy(proof[i:], minerAddr.Bytes())
+
+	return proof, nil
+}
+
+// mockWpostProof generates a mock "window post" proof tied to the specified proof type, and the
+// given miner.
+func mockWpostProof(proofType abi.RegisteredPoStProof, minerAddr address.Address) ([]byte, error) {
+	plen, err := proofType.ProofSize()
+	if err != nil {
+		return nil, err
+	}
+	proof := make([]byte, plen)
+	i := copy(proof, mockPoStProofPrefix)
+	i += copy(proof[i:], minerAddr.Bytes())
+	return proof, nil
+}
+
+// TODO: dedup
+func aggProofLen(nproofs int) int {
+	switch {
+	case nproofs <= 8:
+		return 11220
+	case nproofs <= 16:
+		return 14196
+	case nproofs <= 32:
+		return 17172
+	case nproofs <= 64:
+		return 20148
+	case nproofs <= 128:
+		return 23124
+	case nproofs <= 256:
+		return 26100
+	case nproofs <= 512:
+		return 29076
+	case nproofs <= 1024:
+		return 32052
+	case nproofs <= 2048:
+		return 35028
+	case nproofs <= 4096:
+		return 38004
+	case nproofs <= 8192:
+		return 40980
+	default:
+		panic("too many proofs")
+	}
+}
diff --git a/cmd/lotus-sim/simulation/node.go b/cmd/lotus-sim/simulation/node.go
index 505f563e9..fa4d71028 100644
--- a/cmd/lotus-sim/simulation/node.go
+++ b/cmd/lotus-sim/simulation/node.go
@@ -19,6 +19,7 @@ import (
 	"github.com/filecoin-project/lotus/node/repo"
 )
 
+// Node represents the local lotus node, or at least the part of it we care about.
 type Node struct {
 	Repo       repo.LockedRepo
 	Blockstore blockstore.Blockstore
@@ -26,6 +27,7 @@ type Node struct {
 	Chainstore *store.ChainStore
 }
 
+// OpenNode opens the local lotus node for writing. This will fail if the node is online.
 func OpenNode(ctx context.Context, path string) (*Node, error) {
 	var node Node
 	r, err := repo.NewFS(path)
@@ -55,6 +57,7 @@ func OpenNode(ctx context.Context, path string) (*Node, error) {
 	return &node, nil
 }
 
+// Close cleanly close the node. Please call this on shutdown to make sure everything is flushed.
 func (nd *Node) Close() error {
 	var err error
 	if closer, ok := nd.Blockstore.(io.Closer); ok && closer != nil {
@@ -69,6 +72,7 @@ func (nd *Node) Close() error {
 	return err
 }
 
+// LoadSim loads
 func (nd *Node) LoadSim(ctx context.Context, name string) (*Simulation, error) {
 	sim := &Simulation{
 		Node: nd,
@@ -103,6 +107,10 @@ func (nd *Node) LoadSim(ctx context.Context, name string) (*Simulation, error) {
 	return sim, nil
 }
 
+// Create creates a new simulation.
+//
+// - This will fail if a simulation already exists with the given name.
+// - Name must not contain a '/'.
 func (nd *Node) CreateSim(ctx context.Context, name string, head *types.TipSet) (*Simulation, error) {
 	if strings.Contains(name, "/") {
 		return nil, xerrors.Errorf("simulation name %q cannot contain a '/'", name)
@@ -125,6 +133,7 @@ func (nd *Node) CreateSim(ctx context.Context, name string, head *types.TipSet)
 	return sim, nil
 }
 
+// ListSims lists all simulations.
 func (nd *Node) ListSims(ctx context.Context) ([]string, error) {
 	prefix := simulationPrefix.ChildString("head").String()
 	items, err := nd.MetadataDS.Query(query.Query{
@@ -153,6 +162,9 @@ func (nd *Node) ListSims(ctx context.Context) ([]string, error) {
 	}
 }
 
+// DeleteSim deletes a simulation and all related metadata.
+//
+// NOTE: This function does not delete associated messages, blocks, or chain state.
 func (nd *Node) DeleteSim(ctx context.Context, name string) error {
 	// TODO: make this a bit more generic?
 	keys := []datastore.Key{
diff --git a/cmd/lotus-sim/simulation/power.go b/cmd/lotus-sim/simulation/power.go
index 9a64c3f3a..a86b691f3 100644
--- a/cmd/lotus-sim/simulation/power.go
+++ b/cmd/lotus-sim/simulation/power.go
@@ -12,10 +12,6 @@ import (
 	"github.com/filecoin-project/lotus/chain/actors/builtin/power"
 )
 
-type powerInfo struct {
-	powerLookback, powerNow abi.StoragePower
-}
-
 // Load all power claims at the given height.
 func (sim *Simulation) loadClaims(ctx context.Context, height abi.ChainEpoch) (map[address.Address]power.Claim, error) {
 	powerTable := make(map[address.Address]power.Claim)
diff --git a/cmd/lotus-sim/simulation/precommit.go b/cmd/lotus-sim/simulation/precommit.go
index 1ede3d5c4..055918c8c 100644
--- a/cmd/lotus-sim/simulation/precommit.go
+++ b/cmd/lotus-sim/simulation/precommit.go
@@ -20,15 +20,17 @@ import (
 	tutils "github.com/filecoin-project/specs-actors/v5/support/testing"
 )
 
-func makeCommR(minerAddr address.Address, sno abi.SectorNumber) cid.Cid {
-	return tutils.MakeCID(fmt.Sprintf("%s:%d", minerAddr, sno), &miner5.SealedCIDPrefix)
-}
-
 var (
 	targetFunds = abi.TokenAmount(types.MustParseFIL("1000FIL"))
 	minFunds    = abi.TokenAmount(types.MustParseFIL("100FIL"))
 )
 
+// makeCommR generates a "fake" but valid CommR for a sector. It is unique for the given sector/miner.
+func makeCommR(minerAddr address.Address, sno abi.SectorNumber) cid.Cid {
+	return tutils.MakeCID(fmt.Sprintf("%s:%d", minerAddr, sno), &miner5.SealedCIDPrefix)
+}
+
+// packPreCommits packs pre-commit messages until the block is full.
 func (ss *simulationState) packPreCommits(ctx context.Context, cb packFunc) (full bool, _err error) {
 	var top1Count, top10Count, restCount int
 	defer func() {
@@ -50,6 +52,13 @@ func (ss *simulationState) packPreCommits(ctx context.Context, cb packFunc) (ful
 			minerAddr address.Address
 			count     *int
 		)
+
+		// We pre-commit for the top 1%, 10%, and the of the network 1/3rd of the time each.
+		// This won't yeild the most accurate distribution... but it'll give us a good
+		// enough distribution.
+
+		// NOTE: We submit at most _one_ 819 sector batch per-miner per-block. See the
+		// comment on packPreCommitsMiner for why. We should fix this.
 		switch {
 		case (i%3) <= 0 && top1Miners < ss.minerDist.top1.len():
 			count = &top1Count
@@ -67,6 +76,7 @@ func (ss *simulationState) packPreCommits(ctx context.Context, cb packFunc) (ful
 			// Well, we've run through all miners.
 			return false, nil
 		}
+
 		added, full, err := ss.packPreCommitsMiner(ctx, cb, minerAddr, maxProveCommitBatchSize)
 		if err != nil {
 			return false, xerrors.Errorf("failed to pack precommits for miner %s: %w", minerAddr, err)
@@ -78,7 +88,10 @@ func (ss *simulationState) packPreCommits(ctx context.Context, cb packFunc) (ful
 	}
 }
 
+// packPreCommitsMiner packs count pre-commits for the given miner. This should only be called once
+// per-miner, per-epoch to avoid packing multiple pre-commits with the same sector numbers.
 func (ss *simulationState) packPreCommitsMiner(ctx context.Context, cb packFunc, minerAddr address.Address, count int) (int, bool, error) {
+	// Load everything.
 	epoch := ss.nextEpoch()
 	nv := ss.sm.GetNtwkVersion(ctx, epoch)
 	st, err := ss.stateTree(ctx)
@@ -120,6 +133,7 @@ func (ss *simulationState) packPreCommitsMiner(ctx context.Context, cb packFunc,
 		}
 	}
 
+	// Generate pre-commits.
 	sealType, err := miner.PreferredSealProofTypeFromWindowPoStType(
 		nv, minerInfo.WindowPoStProofType,
 	)
@@ -143,6 +157,8 @@ func (ss *simulationState) packPreCommitsMiner(ctx context.Context, cb packFunc,
 			Expiration:    expiration,
 		}
 	}
+
+	// Commit the pre-commits.
 	added := 0
 	if nv >= network.Version13 {
 		targetBatchSize := maxPreCommitBatchSize
@@ -158,6 +174,8 @@ func (ss *simulationState) packPreCommitsMiner(ctx context.Context, cb packFunc,
 			if err != nil {
 				return 0, false, err
 			}
+			// NOTE: just in-case, sendAndFund will "fund" and re-try for any message
+			// that fails due to "insufficient funds".
 			if full, err := sendAndFund(cb, &types.Message{
 				To:     minerAddr,
 				From:   minerInfo.Worker,
diff --git a/cmd/lotus-sim/simulation/provecommit.go b/cmd/lotus-sim/simulation/provecommit.go
index 0d855bcd1..ec0c99c8a 100644
--- a/cmd/lotus-sim/simulation/provecommit.go
+++ b/cmd/lotus-sim/simulation/provecommit.go
@@ -21,7 +21,10 @@ import (
 	power5 "github.com/filecoin-project/specs-actors/v5/actors/builtin/power"
 )
 
+// packProveCOmmits packs all prove-commits for all "ready to be proven" sectors until it fills the
+// block or runs out.
 func (ss *simulationState) packProveCommits(ctx context.Context, cb packFunc) (_full bool, _err error) {
+	// Roll the commitQueue forward.
 	ss.commitQueue.advanceEpoch(ss.nextEpoch())
 
 	var failed, done, unbatched, count int
@@ -64,6 +67,14 @@ type proveCommitResult struct {
 	done, failed, unbatched int
 }
 
+// sendAndFund "packs" the given message, funding the actor if necessary. It:
+//
+// 1. Tries to send the given message.
+// 2. If that fails, it checks to see if the exit code was ErrInsufficientFunds.
+// 3. If so, it sends 1K FIL from the "burnt funds actor" (because we need to send it from
+//    somewhere) and re-tries the message.0
+//
+// NOTE: If the message fails a second time, the funds won't be "unsent".
 func sendAndFund(send packFunc, msg *types.Message) (bool, error) {
 	full, err := send(msg)
 	aerr, ok := err.(aerrors.ActorError)
@@ -87,7 +98,10 @@ func sendAndFund(send packFunc, msg *types.Message) (bool, error) {
 	return send(msg)
 }
 
-// Enqueue a single prove commit from the given miner.
+// packProveCommitsMiner enqueues a prove commits from the given miner until it runs out of
+// available prove-commits, batching as much as possible.
+//
+// This function will fund as necessary from the "burnt funds actor" (look, it's convenient).
 func (ss *simulationState) packProveCommitsMiner(
 	ctx context.Context, cb packFunc, minerAddr address.Address,
 	pending minerPendingCommits,
@@ -200,7 +214,10 @@ func (ss *simulationState) packProveCommitsMiner(
 	return res, false, nil
 }
 
-// Enqueue all pending prove-commits for the given miner.
+// loadProveCommitsMiner enqueue all pending prove-commits for the given miner. This is called on
+// load to populate the commitQueue and should not need to be called later.
+//
+// It will drop any pre-commits that have already expired.
 func (ss *simulationState) loadProveCommitsMiner(ctx context.Context, addr address.Address, minerState miner.State) error {
 	// Find all pending prove commits and group by proof type. Really, there should never
 	// (except during upgrades be more than one type.
diff --git a/cmd/lotus-sim/simulation/simulation.go b/cmd/lotus-sim/simulation/simulation.go
index 384cc79cb..dc5cb3976 100644
--- a/cmd/lotus-sim/simulation/simulation.go
+++ b/cmd/lotus-sim/simulation/simulation.go
@@ -2,10 +2,7 @@ package simulation
 
 import (
 	"context"
-	"crypto/sha256"
-	"encoding/binary"
 	"encoding/json"
-	"time"
 
 	"golang.org/x/xerrors"
 
@@ -13,9 +10,7 @@ import (
 	logging "github.com/ipfs/go-log/v2"
 
 	"github.com/filecoin-project/go-state-types/abi"
-	"github.com/filecoin-project/go-state-types/crypto"
 	"github.com/filecoin-project/go-state-types/network"
-	"github.com/filecoin-project/lotus/build"
 	"github.com/filecoin-project/lotus/chain/actors/builtin"
 	"github.com/filecoin-project/lotus/chain/state"
 	"github.com/filecoin-project/lotus/chain/stmgr"
@@ -35,16 +30,23 @@ const (
 	maxProveCommitBatchSize = miner5.MaxAggregatedSectors
 )
 
+// config is the simulation's config, persisted to the local metadata store and loaded on start.
+//
+// See simulationState.loadConfig and simulationState.saveConfig.
 type config struct {
 	Upgrades map[network.Version]abi.ChainEpoch
 }
 
+// upgradeSchedule constructs an stmgr.StateManager upgrade schedule, overriding any network upgrade
+// epochs as specified in the config.
 func (c *config) upgradeSchedule() (stmgr.UpgradeSchedule, error) {
 	upgradeSchedule := stmgr.DefaultUpgradeSchedule()
 	expected := make(map[network.Version]struct{}, len(c.Upgrades))
 	for nv := range c.Upgrades {
 		expected[nv] = struct{}{}
 	}
+
+	// Update network upgrade epochs.
 	newUpgradeSchedule := upgradeSchedule[:0]
 	for _, upgrade := range upgradeSchedule {
 		if height, ok := c.Upgrades[upgrade.Network]; ok {
@@ -56,6 +58,8 @@ func (c *config) upgradeSchedule() (stmgr.UpgradeSchedule, error) {
 		}
 		newUpgradeSchedule = append(newUpgradeSchedule, upgrade)
 	}
+
+	// Make sure we didn't try to configure an unknown network version.
 	if len(expected) > 0 {
 		missing := make([]network.Version, 0, len(expected))
 		for nv := range expected {
@@ -63,9 +67,16 @@ func (c *config) upgradeSchedule() (stmgr.UpgradeSchedule, error) {
 		}
 		return nil, xerrors.Errorf("unknown network versions %v in config", missing)
 	}
+
+	// Finally, validate it. This ensures we don't change the order of the upgrade or anything
+	// like that.
+	if err := newUpgradeSchedule.Validate(); err != nil {
+		return nil, err
+	}
 	return newUpgradeSchedule, nil
 }
 
+// Simulation specifies a lotus-sim simulation.
 type Simulation struct {
 	*Node
 
@@ -82,6 +93,8 @@ type Simulation struct {
 	state *simulationState
 }
 
+// loadConfig loads a simulation's config from the datastore. This must be called on startup and may
+// be called to restore the config from-disk.
 func (sim *Simulation) loadConfig() error {
 	configBytes, err := sim.MetadataDS.Get(sim.key("config"))
 	if err == nil {
@@ -97,6 +110,18 @@ func (sim *Simulation) loadConfig() error {
 	return nil
 }
 
+// saveConfig saves the current config to the datastore. This must be called whenever the config is
+// changed.
+func (sim *Simulation) saveConfig() error {
+	buf, err := json.Marshal(sim.config)
+	if err != nil {
+		return err
+	}
+	return sim.MetadataDS.Put(sim.key("config"), buf)
+}
+
+// stateTree returns the current state-tree for the current head, computing the tipset if necessary.
+// The state-tree is cached until the head is changed.
 func (sim *Simulation) stateTree(ctx context.Context) (*state.StateTree, error) {
 	if sim.st == nil {
 		st, _, err := sim.sm.TipSetState(ctx, sim.head)
@@ -128,6 +153,8 @@ func (sim *Simulation) simState(ctx context.Context) (*simulationState, error) {
 
 var simulationPrefix = datastore.NewKey("/simulation")
 
+// key returns the the key in the form /simulation/<subkey>/<simulation-name>. For example,
+// /simulation/head/default.
 func (sim *Simulation) key(subkey string) datastore.Key {
 	return simulationPrefix.ChildString(subkey).ChildString(sim.name)
 }
@@ -139,14 +166,18 @@ func (sim *Simulation) Load(ctx context.Context) error {
 	return err
 }
 
+// GetHead returns the current simulation head.
 func (sim *Simulation) GetHead() *types.TipSet {
 	return sim.head
 }
 
+// GetNetworkVersion returns the current network version for the simulation.
 func (sim *Simulation) GetNetworkVersion() network.Version {
 	return sim.sm.GetNtwkVersion(context.TODO(), sim.head.Height())
 }
 
+// SetHead updates the current head of the simulation and stores it in the metadata store. This is
+// called for every Simulation.Step.
 func (sim *Simulation) SetHead(head *types.TipSet) error {
 	if err := sim.MetadataDS.Put(sim.key("head"), head.Key().Bytes()); err != nil {
 		return xerrors.Errorf("failed to store simulation head: %w", err)
@@ -156,85 +187,14 @@ func (sim *Simulation) SetHead(head *types.TipSet) error {
 	return nil
 }
 
+// Name returns the simulation's name.
 func (sim *Simulation) Name() string {
 	return sim.name
 }
 
-func (sim *Simulation) postChainCommitInfo(ctx context.Context, epoch abi.ChainEpoch) (abi.Randomness, error) {
-	commitRand, err := sim.Chainstore.GetChainRandomness(
-		ctx, sim.head.Cids(), crypto.DomainSeparationTag_PoStChainCommit, epoch, nil, true)
-	return commitRand, err
-}
-
-const beaconPrefix = "mockbeacon:"
-
-func (sim *Simulation) nextBeaconEntries() []types.BeaconEntry {
-	parentBeacons := sim.head.Blocks()[0].BeaconEntries
-	lastBeacon := parentBeacons[len(parentBeacons)-1]
-	beaconRound := lastBeacon.Round + 1
-
-	buf := make([]byte, len(beaconPrefix)+8)
-	copy(buf, beaconPrefix)
-	binary.BigEndian.PutUint64(buf[len(beaconPrefix):], beaconRound)
-	beaconRand := sha256.Sum256(buf)
-	return []types.BeaconEntry{{
-		Round: beaconRound,
-		Data:  beaconRand[:],
-	}}
-}
-
-func (sim *Simulation) nextTicket() *types.Ticket {
-	newProof := sha256.Sum256(sim.head.MinTicket().VRFProof)
-	return &types.Ticket{
-		VRFProof: newProof[:],
-	}
-}
-
-func (sim *Simulation) makeTipSet(ctx context.Context, messages []*types.Message) (*types.TipSet, error) {
-	parentTs := sim.head
-	parentState, parentRec, err := sim.sm.TipSetState(ctx, parentTs)
-	if err != nil {
-		return nil, xerrors.Errorf("failed to compute parent tipset: %w", err)
-	}
-	msgsCid, err := sim.storeMessages(ctx, messages)
-	if err != nil {
-		return nil, xerrors.Errorf("failed to store block messages: %w", err)
-	}
-
-	uts := parentTs.MinTimestamp() + build.BlockDelaySecs
-
-	blks := []*types.BlockHeader{{
-		Miner:                 parentTs.MinTicketBlock().Miner, // keep reusing the same miner.
-		Ticket:                sim.nextTicket(),
-		BeaconEntries:         sim.nextBeaconEntries(),
-		Parents:               parentTs.Cids(),
-		Height:                parentTs.Height() + 1,
-		ParentStateRoot:       parentState,
-		ParentMessageReceipts: parentRec,
-		Messages:              msgsCid,
-		ParentBaseFee:         baseFee,
-		Timestamp:             uts,
-		ElectionProof:         &types.ElectionProof{WinCount: 1},
-	}}
-	err = sim.Chainstore.PersistBlockHeaders(blks...)
-	if err != nil {
-		return nil, xerrors.Errorf("failed to persist block headers: %w", err)
-	}
-	newTipSet, err := types.NewTipSet(blks)
-	if err != nil {
-		return nil, xerrors.Errorf("failed to create new tipset: %w", err)
-	}
-	now := time.Now()
-	_, _, err = sim.sm.TipSetState(ctx, newTipSet)
-	if err != nil {
-		return nil, xerrors.Errorf("failed to compute new tipset: %w", err)
-	}
-	duration := time.Since(now)
-	log.Infow("computed tipset", "duration", duration, "height", newTipSet.Height())
-
-	return newTipSet, nil
-}
-
+// SetUpgradeHeight sets the height of the given network version change (and saves the config).
+//
+// This fails if the specified epoch has already passed or the new upgrade schedule is invalid.
 func (sim *Simulation) SetUpgradeHeight(nv network.Version, epoch abi.ChainEpoch) (_err error) {
 	if epoch <= sim.head.Height() {
 		return xerrors.Errorf("cannot set upgrade height in the past (%d <= %d)", epoch, sim.head.Height())
@@ -269,6 +229,7 @@ func (sim *Simulation) SetUpgradeHeight(nv network.Version, epoch abi.ChainEpoch
 	return nil
 }
 
+// ListUpgrades returns any future network upgrades.
 func (sim *Simulation) ListUpgrades() (stmgr.UpgradeSchedule, error) {
 	upgrades, err := sim.config.upgradeSchedule()
 	if err != nil {
@@ -283,11 +244,3 @@ func (sim *Simulation) ListUpgrades() (stmgr.UpgradeSchedule, error) {
 	}
 	return pending, nil
 }
-
-func (sim *Simulation) saveConfig() error {
-	buf, err := json.Marshal(sim.config)
-	if err != nil {
-		return err
-	}
-	return sim.MetadataDS.Put(sim.key("config"), buf)
-}
diff --git a/cmd/lotus-sim/simulation/state.go b/cmd/lotus-sim/simulation/state.go
index ee664166e..88971c9f0 100644
--- a/cmd/lotus-sim/simulation/state.go
+++ b/cmd/lotus-sim/simulation/state.go
@@ -2,7 +2,6 @@ package simulation
 
 import (
 	"context"
-	"math/rand"
 	"sort"
 
 	"github.com/filecoin-project/go-address"
@@ -11,41 +10,19 @@ import (
 	"github.com/filecoin-project/lotus/chain/types"
 )
 
-type perm struct {
-	miners []address.Address
-	offset int
-}
-
-func (p *perm) shuffle() {
-	rand.Shuffle(len(p.miners), func(i, j int) {
-		p.miners[i], p.miners[j] = p.miners[j], p.miners[i]
-	})
-}
-
-func (p *perm) next() address.Address {
-	next := p.miners[p.offset]
-	p.offset++
-	p.offset %= len(p.miners)
-	return next
-}
-
-func (p *perm) add(addr address.Address) {
-	p.miners = append(p.miners, addr)
-}
-
-func (p *perm) len() int {
-	return len(p.miners)
-}
-
+// simualtionState holds the "state" of the simulation. This is split from the Simulation type so we
+// can load it on-dempand if and when we need to actually _run_ the simualation. Loading the
+// simulation state requires walking all active miners.
 type simulationState struct {
 	*Simulation
 
+	// The tiers represent the top 1%, top 10%, and everyone else. When sealing sectors, we seal
+	// a group of sectors for the top 1%, a group (half that size) for the top 10%, and one
+	// sector for everyone else. We determine these rates by looking at two power tables.
 	// TODO Ideally we'd "learn" this distribution from the network. But this is good enough for
-	// now. The tiers represent the top 1%, top 10%, and everyone else. When sealing sectors, we
-	// seal a group of sectors for the top 1%, a group (half that size) for the top 10%, and one
-	// sector for everyone else. We really should pick a better algorithm.
+	// now.
 	minerDist struct {
-		top1, top10, rest perm
+		top1, top10, rest actorIter
 	}
 
 	// We track the window post periods per miner and assume that no new miners are ever added.
@@ -58,6 +35,9 @@ type simulationState struct {
 	pendingWposts  []*types.Message
 	nextWpostEpoch abi.ChainEpoch
 
+	// We track the set of pending commits. On simulation load, and when a new pre-commit is
+	// added to the chain, we put the commit in this queue. advanceEpoch(currentEpoch) should be
+	// called on this queue at every epoch before using it.
 	commitQueue commitQueue
 }
 
@@ -167,7 +147,7 @@ func loadSimulationState(ctx context.Context, sim *Simulation) (*simulationState
 	})
 
 	for i, oi := range sealList {
-		var dist *perm
+		var dist *actorIter
 		if i < len(sealList)/100 {
 			dist = &state.minerDist.top1
 		} else if i < len(sealList)/10 {
@@ -185,6 +165,35 @@ func loadSimulationState(ctx context.Context, sim *Simulation) (*simulationState
 	return state, nil
 }
 
+// nextEpoch returns the next epoch (head+1).
 func (ss *simulationState) nextEpoch() abi.ChainEpoch {
 	return ss.GetHead().Height() + 1
 }
+
+// getMinerInfo returns the miner's cached info.
+//
+// NOTE: we assume that miner infos won't change. We'll need to fix this if we start supporting arbitrary message.
+func (ss *simulationState) getMinerInfo(ctx context.Context, addr address.Address) (*miner.MinerInfo, error) {
+	minerInfo, ok := ss.minerInfos[addr]
+	if !ok {
+		st, err := ss.stateTree(ctx)
+		if err != nil {
+			return nil, err
+		}
+		act, err := st.GetActor(addr)
+		if err != nil {
+			return nil, err
+		}
+		minerState, err := miner.Load(ss.Chainstore.ActorStore(ctx), act)
+		if err != nil {
+			return nil, err
+		}
+		info, err := minerState.Info()
+		if err != nil {
+			return nil, err
+		}
+		minerInfo = &info
+		ss.minerInfos[addr] = minerInfo
+	}
+	return minerInfo, nil
+}
diff --git a/cmd/lotus-sim/simulation/step.go b/cmd/lotus-sim/simulation/step.go
index b44f3be4d..79ace1db2 100644
--- a/cmd/lotus-sim/simulation/step.go
+++ b/cmd/lotus-sim/simulation/step.go
@@ -20,6 +20,8 @@ import (
 )
 
 const (
+	// The number of expected blocks in a tipset. We use this to determine how much gas a tipset
+	// has.
 	expectedBlocks = 5
 	// TODO: This will produce invalid blocks but it will accurately model the amount of gas
 	// we're willing to use per-tipset.
@@ -42,6 +44,7 @@ func (sim *Simulation) Step(ctx context.Context) (*types.TipSet, error) {
 	return ts, nil
 }
 
+// step steps the simulation state forward one step, producing and executing a new tipset.
 func (ss *simulationState) step(ctx context.Context) (*types.TipSet, error) {
 	log.Infow("step", "epoch", ss.head.Height()+1)
 	messages, err := ss.popNextMessages(ctx)
@@ -59,20 +62,25 @@ func (ss *simulationState) step(ctx context.Context) (*types.TipSet, error) {
 }
 
 type packFunc func(*types.Message) (full bool, err error)
-type messageGenerator func(ctx context.Context, cb packFunc) (full bool, err error)
 
+// popNextMessages generates/picks a set of messages to be included in the next block.
+//
+// - This function is destructive and should only be called once per epoch.
+// - This function does not store anything in the repo.
+// - This function handles all gas estimation. The returned messages should all fit in a single
+//   block.
 func (ss *simulationState) popNextMessages(ctx context.Context) ([]*types.Message, error) {
 	parentTs := ss.head
-	parentState, _, err := ss.sm.TipSetState(ctx, parentTs)
-	if err != nil {
-		return nil, err
-	}
+
+	// First we make sure we don't have an upgrade at this epoch. If we do, we return no
+	// messages so we can just create an empty block at that epoch.
+	//
+	// This isn't what the network does, but it makes things easier. Otherwise, we'd need to run
+	// migrations before this epoch and I'd rather not deal with that.
 	nextHeight := parentTs.Height() + 1
 	prevVer := ss.sm.GetNtwkVersion(ctx, nextHeight-1)
 	nextVer := ss.sm.GetNtwkVersion(ctx, nextHeight)
 	if nextVer != prevVer {
-		// So... we _could_ actually run the migration, but that's a pain. It's easier to
-		// just have an empty block then let the state manager run the migration as normal.
 		log.Warnw("packing no messages for version upgrade block",
 			"old", prevVer,
 			"new", nextVer,
@@ -81,10 +89,20 @@ func (ss *simulationState) popNextMessages(ctx context.Context) ([]*types.Messag
 		return nil, nil
 	}
 
-	// Then we need to execute messages till we run out of gas. Those messages will become the
-	// block's messages.
+	// Next, we compute the state for the parent tipset. In practice, this will likely be
+	// cached.
+	parentState, _, err := ss.sm.TipSetState(ctx, parentTs)
+	if err != nil {
+		return nil, err
+	}
+
+	// Then we construct a VM to execute messages for gas estimation.
+	//
+	// Most parts of this VM are "real" except:
+	// 1. We don't charge a fee.
+	// 2. The runtime has "fake" proof logic.
+	// 3. We don't actually save any of the results.
 	r := store.NewChainRand(ss.sm.ChainStore(), parentTs.Cids())
-	// TODO: Factor this out maybe?
 	vmopt := &vm.VMOpts{
 		StateBase:      parentState,
 		Epoch:          nextHeight,
@@ -100,9 +118,15 @@ func (ss *simulationState) popNextMessages(ctx context.Context) ([]*types.Messag
 	if err != nil {
 		return nil, err
 	}
-	// TODO: This is the wrong store and may not include important state for what we're doing
-	// here....
-	// Maybe we just track nonces separately? Yeah, probably better that way.
+
+	// Next we define a helper function for "pushing" messages. This is the function that will
+	// be passed to the "pack" functions.
+	//
+	// It.
+	//
+	// 1. Tries to execute the message on-top-of the already pushed message.
+	// 2. Is careful to revert messages on failure to avoid nasties like nonce-gaps.
+	// 3. Resolves IDs as necessary, fills in missing parts of the message, etc.
 	vmStore := vmi.ActorStore(ctx)
 	var gasTotal int64
 	var messages []*types.Message
@@ -181,16 +205,52 @@ func (ss *simulationState) popNextMessages(ctx context.Context) ([]*types.Messag
 		messages = append(messages, msg)
 		return false, nil
 	}
-	for _, mgen := range []messageGenerator{ss.packWindowPoSts, ss.packProveCommits, ss.packPreCommits} {
-		if full, err := mgen(ctx, tryPushMsg); err != nil {
-			name := runtime.FuncForPC(reflect.ValueOf(mgen).Pointer()).Name()
-			lastDot := strings.LastIndexByte(name, '.')
-			fName := name[lastDot+1 : len(name)-3]
-			return nil, xerrors.Errorf("when packing messages with %s: %w", fName, err)
-		} else if full {
-			break
-		}
+
+	// Finally, we generate a set of messages to be included in
+	if err := ss.packMessages(ctx, tryPushMsg); err != nil {
+		return nil, err
 	}
 
 	return messages, nil
 }
+
+// functionName extracts the name of given function.
+func functionName(fn interface{}) string {
+	name := runtime.FuncForPC(reflect.ValueOf(fn).Pointer()).Name()
+	lastDot := strings.LastIndexByte(name, '.')
+	if lastDot >= 0 {
+		name = name[lastDot+1 : len(name)-3]
+	}
+	lastDash := strings.LastIndexByte(name, '-')
+	if lastDash > 0 {
+		name = name[:lastDash]
+	}
+	return name
+}
+
+// packMessages packs messages with the given packFunc until the block is full (packFunc returns
+// true).
+// TODO: Make this more configurable for other simulations.
+func (ss *simulationState) packMessages(ctx context.Context, cb packFunc) error {
+	type messageGenerator func(ctx context.Context, cb packFunc) (full bool, err error)
+
+	// We pack messages in-order:
+	// 1. Any window posts. We pack window posts as soon as the deadline opens to ensure we only
+	//    miss them if/when we run out of chain bandwidth.
+	// 2. Prove commits. We do this eagerly to ensure they don't expire.
+	// 3. Finally, we fill the rest of the space with pre-commits.
+	messageGenerators := []messageGenerator{
+		ss.packWindowPoSts,
+		ss.packProveCommits,
+		ss.packPreCommits,
+	}
+
+	for _, mgen := range messageGenerators {
+		if full, err := mgen(ctx, cb); err != nil {
+			return xerrors.Errorf("when packing messages with %s: %w", functionName(mgen), err)
+		} else if full {
+			break
+		}
+	}
+	return nil
+}
diff --git a/cmd/lotus-sim/simulation/wdpost.go b/cmd/lotus-sim/simulation/wdpost.go
index 7abb9a83a..fe93a5f0c 100644
--- a/cmd/lotus-sim/simulation/wdpost.go
+++ b/cmd/lotus-sim/simulation/wdpost.go
@@ -5,41 +5,29 @@ import (
 	"math"
 	"time"
 
+	"golang.org/x/xerrors"
+
 	"github.com/filecoin-project/go-address"
 	"github.com/filecoin-project/go-state-types/abi"
+	"github.com/filecoin-project/go-state-types/crypto"
+
 	"github.com/filecoin-project/lotus/chain/actors"
 	"github.com/filecoin-project/lotus/chain/actors/aerrors"
 	"github.com/filecoin-project/lotus/chain/actors/builtin/miner"
 	"github.com/filecoin-project/lotus/chain/types"
+
 	proof5 "github.com/filecoin-project/specs-actors/v5/actors/runtime/proof"
-	"golang.org/x/xerrors"
 )
 
-func (ss *simulationState) getMinerInfo(ctx context.Context, addr address.Address) (*miner.MinerInfo, error) {
-	minerInfo, ok := ss.minerInfos[addr]
-	if !ok {
-		st, err := ss.stateTree(ctx)
-		if err != nil {
-			return nil, err
-		}
-		act, err := st.GetActor(addr)
-		if err != nil {
-			return nil, err
-		}
-		minerState, err := miner.Load(ss.Chainstore.ActorStore(ctx), act)
-		if err != nil {
-			return nil, err
-		}
-		info, err := minerState.Info()
-		if err != nil {
-			return nil, err
-		}
-		minerInfo = &info
-		ss.minerInfos[addr] = minerInfo
-	}
-	return minerInfo, nil
+// postChainCommitInfo returns th
+func (sim *Simulation) postChainCommitInfo(ctx context.Context, epoch abi.ChainEpoch) (abi.Randomness, error) {
+	commitRand, err := sim.Chainstore.GetChainRandomness(
+		ctx, sim.head.Cids(), crypto.DomainSeparationTag_PoStChainCommit, epoch, nil, true)
+	return commitRand, err
 }
 
+// packWindowPoSts packs window posts until either the block is full or all healty sectors
+// have been proven. It does not recover sectors.
 func (ss *simulationState) packWindowPoSts(ctx context.Context, cb packFunc) (full bool, _err error) {
 	// Push any new window posts into the queue.
 	if err := ss.queueWindowPoSts(ctx); err != nil {
@@ -84,7 +72,7 @@ func (ss *simulationState) packWindowPoSts(ctx context.Context, cb packFunc) (fu
 	return false, nil
 }
 
-// Enqueue all missing window posts for the current epoch for the given miner.
+// stepWindowPoStsMiner enqueues all missing window posts for the current epoch for the given miner.
 func (ss *simulationState) stepWindowPoStsMiner(
 	ctx context.Context,
 	addr address.Address, minerState miner.State,
@@ -198,7 +186,8 @@ func (ss *simulationState) stepWindowPoStsMiner(
 	return nil
 }
 
-// Enqueue missing window posts for all miners with deadlines opening at the current epoch.
+// queueWindowPoSts enqueues missing window posts for all miners with deadlines opening between the
+// last epoch in which this function was called and the current epoch (head+1).
 func (ss *simulationState) queueWindowPoSts(ctx context.Context) error {
 	targetHeight := ss.nextEpoch()