I should have done this earlier. Now I have, and I think what it tells me is that the angle of the rear window may not be all that bad for air flow. In the linked video, you will see what I think is mostly pretty good flow down the window. A little turbulent, maybe? But down low, in the center, you'll see tufts that are being sucked-up the windowpane. That movement was very consistent, at 40 as much as 65 mph. The bottom row of tufts would be under my trunk lid if it were attached.
Thoughts anyone?