Either of the red/orange line roof extensions could be added to the project. The blue line, with side panels, is not yet giving any aero improvement.
The upper line is closer to the template. The lower line would be far easier to build.
The upper, longer roof extension option would likely require several supports as it would be over a foot, front to rear. I have a piece of coroplast that could be made into the lower red line. Building the upper line would mean buying more coroplast. Would also require more support structure as the panel would be more than a foot, front to rear. Or I might make the upper line of 2.7 mm. lauan plywood, which is much stiffer than coroplast.
Re. the upper line option - which I think holds more potential since it's closer to the template - its leading edge would lay on the roof, would be taped down during testing. There's a limit to how much I can shave or bevel the material's leading edge to reduce the height of the joint. Will air flow separation be a problem there? On the lower line option, the leading edge would be butted up against the window molding so that should not be an issue.
aerohead, any thoughts?