A knowledge management system chunks documents into 512-token chunks with 50-token overlap. Users ask questions that require synthesizing information spread across 8-10 chunks. Retrieved chunks are limited to top-5 by default. Engineers increase top-k to 20 to capture more chunks but find answer quality degrades because the LLM context is now full of marginally relevant chunks. What retrieval architecture addresses this more effectively?

B is correct because the problem is retrieval precision: ANN vector search retrieves semantically plausible candidates but lacks the fine-grained relevance discrimination needed to distinguish essential chunks from marginally relevant ones. A cross-encoder reranker evaluates query-document relevance with full attention over both, producing much higher precision scores. Running it over 50 first-stage candidates and passing only the top-10 reranked results to the LLM gives the LLM a high-precision, high-coverage set. A is wrong because reducing chunk size to 256 tokens means each chunk holds less information; the system would need even more chunks to capture the same content, not fewer, and the precision problem is unchanged. C is wrong because max_tokens controls output length, not input processing; the problem is that marginally relevant input degrades the LLM's synthesis, which is not addressed by allowing longer output. D is wrong because meta-chunk retrieval is a useful approach for document-level selection but does not solve the within-document chunk precision problem; it also requires pre-generating summaries for every document, adding ingestion overhead.