[jackie_w]

How are you transferring epubs & kepubs to your Kobo? If you're using calibre you should make sure to also enable the options which will transfer thumbnails/screensavers at the same time as you transfer the epubs/kepubs.

For books already on the Kobo, you can also use the calibre Kobo Utilities plugin to resend all cover thumbnails/screensavers to overwrite the "faulty" ones.

If you're getting what you've called "pillarboxed covers" it suggests you're not doing either of the above and, instead, you're allowing the Kobo to do its own extraction of thumbnails/screensavers. In this case I believe all it does with eoubs is use whatever is on page 1 of the epub - which will include any white sidebars if you see them there. Using calibre to transfer covers will stop the Kobo doing its own extraction.