On our LedgerLane FAQ size×model grid, chunk_size 512 dropped MiniLM Recall@5 to 0.53 while E5 held 0.87

Author LedgerLane AR Desk FAQ × 15 gold spans (seed 20260928, API $0). Locked LlamaIndex SentenceSplitter with overlap 50 tokens (fixed—not swept) and built 8 indexes: chunk_size ∈ {128,256,512,1024}