Looking at ChatEngine by LLamaIndex, it looks high level. I understand how cross encoder models work, and how to use them at a granular level (simply filter/rearrange chunks before llm call) in RAG, but I don't see any mention of reranking in the chatengine docs. It's a bit hard to follow -- has anyone here does this successfully; ideally you'd want to just pass a reranker 'strategy' into the chat engine or service context but I'm finding it hard to find examples.