Having larger white areas around the cover would be much worse to me (I don't even like when the SD card shows the white on the sides of the images).
I didn't want to have to edit almost 2k books either to adjust the covers. Even books where the cover page is set to 100% height and width and perspective ratio is set to none still will show the odd format covers differently when on the SD card. Only true 3:4 aspect ratio will show correctly, and haven't been able to figure out another way.
Is there no way on the Glo to include the SD card, but to have the reader ignore it unless you tell it to scan the card?