I guess that's what I was trying to describe jamie, but not very well. It seems that the snow that blows against the rear window is the standing snow that gets scoured off of the cargo cover panels. As that snow blows around during the first few minutes of driving, it hits the window. Once the panels are scoured clean, and the defroster melts that blown snow, no more snow seems to hit the window. All that's left is that little half-pyramid, and that doesn't really bother me.
It was snowing on today's drive to work, but since the truck was in the garage overnight, the cargo panels were clean and dry. When I got to work, the back window was still clear. Not one flake hit it. I tried watching the passing snow to see how it flowed around back there, but couldn't see any.
In my old Blazer, I had to wash the back window every couple of minutes 'cause it collected so much salt and road grime.
My old S-10 pickup before that had a soft tonneau cover, and it also collected snow like the Av hard covers, which also would blow against the back window. However, unlike the Av, once the cover was scoured clean, the fresh falling snow would also collect on the back window. The worst part was chunks of ice: they would collect in the gap between the cab and bed, and get crunched while driving due to chassis flex. Real annoying.
So, is the Av perfect when it comes to snow/dirt on the back window? No, but it's far better than anything else I drove in the past 10 years!
-- SS