I once came up with something similar, but never followed through.
https://ecomodder.com/forum/showthre...a-19525-2.html
Quote:
EDIT 12/16/11
I found a patent somewhat similar to the trail edge/corner thing I've been thinking about. Again, a wing, and not a box (truck cab).
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Sadly the patent links no longer work.
The idea is air passing over the roof is at a different pressure than the side, therefore vortexes start forming at the corners, the reverse cone shape would delay or manage said vortexes in a controlled manner thereby reducing drag.
Aerohead if I recall correctly said such devises would not eliminate vortex formation, but might possibly delay it. To what end no one seems to know for sure.
Maybe the people at Lexus know now?
EDIT:
If you turn the original image upside down, it kind of has an under-tray rear diffuser thing going on.