[freebeard]

While I had seen other New Beetle wing threads, I hadn't seen that one so—thanks.

The similarities are less than you might think. The New Beetle is a lot cleaner below the beltline. Above the beltline, it doesn't have the problematic external rain gutters, but it also doesn't have as much taper in plan. So with the Olde Beetle, there's a point around the rear axle line where separation sets in. You just have to fix from there on back.

As for this design, I wonder what it would perform like if the top edge followed a fastback line forward to the top of the backlight. In the thread, they discuss A-B-A testing the air gap at the front. If it was mounted on kitchen cabinet drawer rollers one could slide it back and forth and see the difference in real time. This is possible because there is no plan taper in his tail assembly at all.

I'm leaning toward a triangular deck below the backlight that extends far back enough that it captures the vortexes streaming off the top of the B-pillar. An interesting test case would be to hang half of a surf board [front or back half, inverted or not] horizontally below the backlight. Even without paneling in underneath; if it impedes the inward half, it might dissipate the vortexes.