With p-books it was certainly the cover that made me notice it (and once in a rare while, a review) and pick it up. Obviously it was the content that sold the book to me, but that first contact is visual. A little less so with e-books - but I do often filter a lot based on how professional the cover looks. I know you shouldn't judge a book by its cover, but I still do anyway.
In your case, all the covers look professional, both before and after images
but as you have noticed youself, some work better in a small size than others. It was interesting to see.