I would agree. My CRX has a steeper hatch angle, yet there has been tuft testing to prove that the air is attached to the hatch. (Which was a selling point to me.)
Example:
I'd go with that last concept you had Razor. You might even look into whether it would be good to taper up that last angle a bit, like the CRX too. ???
Oh, will you be keeping the spare tire on? Your last concept might not allow for one.