I grabbed it out of thin air. It only applies if there is a SQLite persistence store and is ignored otherwise. I figured 20 is roughly the size of most popular paginated APIs responses, or that typical response sizes would be in the 100 range if not paginated. For those it should fit nicely. And when I tested on a response of 100,000 records it seemed to still be a performance improvement over zero batch size being set, so I think it should be fine for now.