theboyk sent me a sample book to look at.
The first thing I did was open it in the calibre viewer and I immediately knew what was wrong. The viewer opened so the page area wasn't in a 3:4 ratio. The cover was stretched. The answer is that you have preserveAspectRatio="none". This means if the image is resized, the aspect ratio is not kept. When the page is displayed on the device, it will be stretched for two reasons: the footer takes up some space and the margin settings you have in the reader.
Changing to use preserveAspectRatio="xMidYMid meet" will fix the problem.
There was some discussion of this in the last few days. Have a look at
https://www.mobileread.com/forums/sho....php?p=2301231.