Starting to go through my pics and vids from my trip to El Mirage for the SCTA event this weekend. My daughter was helper in taking the video that provided these stills. We just went off to a corner of the dry lake bed and let the dust do its thing.
Traveling between 45-50 mph:
and:
and the results collected on the back of the car:
I see evidence of spiraling vortexes off the c-pillars and the trunk lid. And while the dust reaches the trunk lid, it does not collect behind the read widow. And in the wake you can see down wash, with the dust height dropping at first, as the air washes off the rear decklid and hits the ground. Then the dust begins to rise again to a level as high or higher than the decklid in these pics.
In the last pic, you can faintly see dust collected on all the flay surfaces of the emblems. But it is slight. The heaviest layering of dust is on the bumper cover's top and the license plate framing.
The downwash and vortex is the most interesting thing to me here... no boat tails are in my future but I still love the idea of a substantial flat spoiler on the trunk lid. It seems to me it might reduce the power of these vortexes.