That's the loft line. The various aerocaps that have been shown here vary from a square shoulder like the Cybertruck, to increasing tumblehome until the truncation at the tailgate is a curve.
What do you think of combining the two ideas at #18? Or all three including readpoint5's?
https://external-content.duckduckgo.com/iu/?....&ipo=images
Maybe a curved panel half the length of the bed?