I am reading a series of light novels in Moon Reader+. These are in .epub format that have been converted from PDFs. In the older version of Moon Reader+ (about two updates ago), when I opened a file, the full-color cover page was stretched to fill the resolution of my Samsung Galaxy Tab 2.
When the current version of the app is in portrait mode, the cover page does not "fit width", but rather displays it very small.
Here is an example of the same epub cover on two of my devices. The cover shows up larger on my Nook Simple Touch than on my 7" Galaxy Tab 2.