Adding a cover to a book

Hi All

I have several ePub format books on my Mac, and I have found an easy way to convert them to MOBI format using Caliber, then using DropBox to get them onto my iPad and opening in Kindle App.

However, one or two of the books don't have a cover, and I was wondering if there is a way to add a cover in Caliber. I found the Edit Metadata section, got hold of a copy of the required image for a cover, added it within Caliber but when I convert this to MOBI format, I still don't see the cover of the book when I open it in the kindle app on the iPad, just the opening page of text.

Is there a proper way to accomplish this please?

Thanks.