As suggested by mtravellerh I am re-logging this problem in the correct place.
Details here
https://www.mobileread.com/forums/showthread.php?t=83281
In short EPUB images are not being displayed correctly when using AdobeViewer. Images seem to be "over-expanded" meaning:-
- they look worse than they should
- they run off the sides of the screen if they are bigger than a certain size