[Big Dave]

My homemade aerocap was too steep at 17%. But it was easy to make.

I concur that the lower the air dam, the better. The reduction in coefficient is greater than the increase in frontal area. My 1.5" clearance air dam worked great but was a4 karat pain in the butt. My 8" clearance air dam doesn't work at all but doesn't drag things. Maybe 3 or 4 inches might be best.

The study stayed with add-on stuff on a stock bed.

What if the bed itself curved to a 12 degree taper (in the plan view) aft of the wheel wells? The space lost is not highly useful. Dead-cat space IMO.

The tangent of 12 degrees is 0.212. So the top deck of my 80 inch long bed should be about 17 inches below the top of the cab.

My tailgate sits about two feet behind the wheel wells. Using a twelve degree taper that would reduce width by 5 inches on each side or 10 inches overall. That would represent a 12.5% decrease in wake area.