I believe something is wrong with my viewer.
I converted epub to mobi. Epub cover is ok in Calibre viewer, but mobi cover is bigger and distorts when I resize the window. I want it to retain it's aspect ratio. Now I don't know if this has always been so - it is the first time I've looked at mobi file with Calibre viewer. (I have 'maintain aspect ratio' checked in output settings)
Secondly, I modified an epub (in Sigil), and can vouch that cover aspect ratio is xMid... etc . In Calibre viewer, cover is distorted (actually, all big pictures are distorted). About that I'm pretty sure - in my home computer cover aspect does not follow the window.
There must be some setting or tweak...
trav