Neil, I agree with your concern about those wedge shoulders.
Your design is interesting. I like your down-arch shoulders over the tailgate in terms of direction. I just hope flow will attach to it since that club-cab Dakota has a pretty short box. Do you have any plans to find out?
My truck box is 2-3 inches higher in the back than front over a length of 78 inches so ~2 degrees. That probably helped my previous hard tonneau with reattachment.