No, there shouldn't be any white at the top. Place the dustjacket fully into the top edge of the cover. If you do so, there will be no white showing there. When I pull the cover up to create the bottom fold, I pull with both hands upward and create enough tension that the dustjacket just starts to curl up. I then hold that with one hand at the center. I use the bone folder from the center to each edge to crease the cover.
So a tight tuck, a slight curl and a hard crease is all it takes.