RAG Reranker Showdown: Small Cross-Encoder Pushed Correct Chunks Out of Top 5

Affectionate_Slip654 · reddit · 2026-10-26

The author benchmarked four rerankers (Cross-Encoder, LLM-based, Cohere, Jina) on 1,507 chunks from payment-industry PDFs in a full RAG pipeline. Key findings: similarity ≠ relevance; a local mini cross-encoder rewarded word matching and pushed both correct answer chunks out of Top 5; an LLM listwise reranker understood context and ranked them 1st-2nd; Cohere lifted an answer from rank 15 to 1. Cohere and Jina offered the best accuracy/speed balance, at the cost of per-call pricing and sending docs to third parties. Code repo and video walkthrough are public.

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