[hat_man]

If I'm understanding you right Aerohead, the high pressure area is under the half tonneau and trapped there. And IIRC, isn't there an area of low pressure behind a vehicle, created as it punches a hole through the air. And a full aero cap helps make this low pressure area smaller.

Would there be any benefit in "venting" some of that high pressure under the half tonneau (say something like 20%) through a couple of openings in the tailgate (something like two 2" pvc fittings) into that low pressure area to further reduce it?

In my mind I'm seeing a cab wing and half tonneau like in the chart, with two openings at the lowest part of the tailgate nearest the bed. Or even crazier yet, turning the area under the half tonneau into some sort of a modified De Laval nozzle.

p.s. I think my mind has finally wandered way out of the box having to be on the couch with this broken foot. LoL