Too much time staring at things while I drove down the road again this week and realized something. Most of the talk I have seen on here for aero caps for pickup trucks involves basically a flat plane from the roofline to the tailgate (profile view). I commonly see a reference here of 11* being the amount of angle that can maintain connected airflow. So in order to keep more usable room under a cap why don't we look at curved surface instead of flat planes? Using a series of 10* facets we can go from horizontal to vertical in 9 steps. With 3" facets that takes less than 16". If we fair the curve to get rid of the facets we should be able to maintain connected airflow from horizontal to vertical with a minimum intrusion on usable bed space.
I think the cap would want to be as molded to the cab dimensions as possible (curves or not), but in the rear I would think curves would help, yes.
On that note I've been looking at landscaping trailers and wondered why, in the very front of the bed the whole thing is square... Yet another thing it wouldn't take much just to smooth out the corners (less crap to tear up your jeans too lol).
Not that folks with trailers get 50mpg, but a few % improvement is % no matter what.
A FE gauge should be standard equipment in every vehicle.