Are the kwargs for as query engine

not entirely.

They all get passed into both the underlying retriever and response synthesizer (I know I know, kwarg abuse)

And if using a vector index, here's the vector retriever

https://gpt-index.readthedocs.io/en/latest/api_reference/query/retrievers/vector_store.html#llama_index.indices.vector_store.retrievers.retriever.VectorIndexRetriever

Lemme know if you have a specfific question in mind though