[BlackGold6.4]

Originally Posted by aerohead

Where the more-steeply falling roofline of the 'pup' is, technically, that steeper contour is going to create a flow deceleration and pressure increase, exceeding the 'threshold' for which the boundary-layer can remain attached.
It's the 'adverse pressure gradient' taught about in boundary-layer theory, always responsible for flow separation, which in turn is the reason for pressure drag, the main component of aerodynamic drag. To be avoided at all cost.
Lofting that contour back up to where the bedcover contour would continue, would reaccelerate the flow, restore a favorable pressure gradient, reattach the flow, and give you back, the otherwise lost pressure recovery, which will cut drag and rear lift, plus give you a little more useful storage volume.

So during research the steeper back on the cap is what works but for my build it will depend on function and fitting gear required, for example; where the mattress fits above the pull-out gear drawers or how ever it's stored will determine where this sloop at the back sloops to. This will also determine how the pup on the back fits too. I won't have a whale tail out back but as what will fit for gear required while maintaining departure angle.