"Chunking" has a bad history in IR going back through the history of the TREC conference. For instance you might index the whole document or index sections or paragraphs and somehow aggregate the paragraph hits up into document hits. It's one of the many things that doesn't help performance even if you think it did, and it may hurt.

The answer is "make the context window as large as you reasonably can" because you have to have enough (con)text in the window for the system to decide what the words mean and if you don't have enough of it you won't get it right.