Retrieval Lab
One question, three retrievers side by side: keyword search, vector search and their fusion. Each column shows where the answer chunk landed. Change how fusion works and watch the order move.
Used on RAG-27 and RAG-28 and RAG-31 and RAG-32
0 chunks, recursive 512 tokens. Teal edge: the chunk holds the golden evidence. Try g-24 (storm excess) and g-09 (error E1007): each retriever wins one.
What to notice
g-24, “Is there an excess for storm damage?”: BM25 ranks the answer 1, vectors rank it 6, fusion keeps it in the top 3.
Surprise
Fuse only the top 3 of each list and one answer falls out of the top 3 (46 of 47). Changing k from 60 to 1 moves only the storm excess answer.
Try next
Type “laptop theft max” and compare with g-23, the full question. Short queries move ranks both ways.