I too have been having trouble getting the cover image to fill the screen on e-readers. I tried different approaches in HTML/CSS with no success. I tried the
FlightDeck solution, no luck there. Then I found this thread and tried the updated code, but the resulting image was only slightly larger. [Side note: I found the info in this thread very informative.]
I'm currently building an EPUB3 sample book so that I can learn Sigil before moving onto books that will be sold. When viewing the ebook on either a Kindle or Samsung tablet, I get a large white border around the image. The border is thicker along the bottom. I've looked at other ebooks and their covers are full screen, so I know it can be done.
Any help would be appreciated. As I said, I've been attempting to beat this through trial and error, but after a week I'm ready for some help.
[Also, I thought about making a new thread on the subject, but thought this post was inline with the thread I replied to.]
Thanks
Tim