I disagree with Hajo. Take a look at the ePub from the following link and you'll see this is just not always so that you need to know the screen size ahead of time. However, it does help if you have a guess of the possible minimum size of the screen. So if we use a 6" eink screen as that marker, then good reflowing content with a complex layout can be made to look good.
https://www.mobileread.com/forums/att...6&d=1241731327