'beamer:
Not sure if stuff really blew around behind seats 'cause windblocker kept me from putting stuff back there anyway. My "test" for the Mazda windblocker was to see if my baseball cap would stay-put at 70+MPH....made no difference....either way, cap felt like it was on verge of blowing off. Best part about removing windblocker was gaining access to that (small) area behind the seats (in the Miata).
I agree that the windblocker needs to be close to the seatback to be really effective....I was in a Z3 with aftermarket windblocker...it was tall and close to seatbacks and worked quite well.
Honestly, I dislike windblockers, and would not put one in the Spridget: not crazy about the way they look...but I think the clear plastic ones look better than the mesh ones (in my opinion).
One of my planned winter projects involves building a "bikini-top" for the Spridget (like on Jeeps). Front part of this would clip to windshield and rear part will attach to roll bar. Spridget rear windows don't zip out, so this would give me some protection during brutal sunny days...probably cut down on cockpit turbulence too. Surprised they aren't available commercially.