Hope these pics help out. Yes there is a slight angled rise of maybe 1 - 2 inches from the back cargo area where it meets the seat back. You can see in the picture that the seat back will fold flat (if you remove the headrests). In this picture I have moved the front passenger seat all the way forward so you can see the gap between the folded rear seat and frontseat's back.
Should not make to much difference for cargo use, but if you were planning to sleep in this area I would think it would require a thick pad of some type to make up the difference.
Curt