In the inverted index, there is a certain order of documents and in a results set, there is another one.

Now, iterating over the index in the order of a results set means mapping the the order-of-relevance (from the results set) to the order-in-the-index (as sorted by KinoSearch). That involves quite a lot of repositioning of the read pointer (disk seeks) and slows down.

Optimally, I would read doc after doc like they are stored in the invindex and not by an arbitrary order I get via a results-subset. That would cut the seeks and speed up.
But as it seems nobody here (including me) knows how to access KinoSearch inverted indexes directly to interate over the docs in the order they are stored in the index.