I recently borrowed from the library a copy of
Fast Flavours by Michael Smith and much to my horror, I think it has to be a fixed format ePub.
287 xhtml files!
275 image files (many of which are nothing more than a clock face to show complexity of the recipe and an outline of a box to appear below the main recipe and contain some comments.
As far as trying to change font sizes in it or even reading it on (in my case a Kobo Glo) forget about it.
Why on earth do publishers release something and attempt to replicate the look of a print book down to the minutest detail?
I could see this having been done in a PDF maybe (and then I would not have even bothered to borrow it).