EPUB are formatted to a certain page size, usually the same size as the original hardback or paperback but not always.
The page display in the reader is where about in the page you are hence the 38,38-39,39 display.
When you read a Sony lrf/lrx ebook they are formatted such that each page is a separate page so you won't see the partial page display.
Kindles I believe have a location(I think its called this) rather than a page display so you could have 600 locations for a 280 page books for example.
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