[hat_man]

Katch22i you've hit the nail on the head. It is more academic than design. I wouldn't do both levels (red and yellow) at the same time but wasn't sure how to show the different options until the really bad paint diagrams. I was under the same impression that having a larger volume of trapped air would create a slightly lower pressure (higher pressure differential) across the tailgate, but had no clue if my assumptions were correct.

I believe the Ridgeline side rails do cant inward but I don't have a clue at what angle.

So if my hypothetical vehicle did exist having the Ridgeline sail panels and the sloped and canted side rails with the yellow cover would be the more beneficial option, right? It's too bad Honda didn't think of it, but from a selling point of view it probably wouldn't go over anyhow. If they had turned the roll up bed cover around 180° you could almost use it as a half tonneau if it would lock in place there. Or even had the roll up bed cover follow the sloped bed rails. It would have created a larger storage compartment and allowed for at least a downward sloping surface (albeit well below the template) for air coming over the cab to move along. Turning the roll up bed cover 180° and having it lock in place at the halfway point and following the sloped rails might have worked a little better yet.