The screen I made for Dolly is quite low, well below head height, but I put a significant kickout near the top that seems to keep the worst off at sub 70mph. Over that I get a bit of buffeting, but It's rare I travel that fast, unless Mr Hayward is leading ;-) I moulded it from perspex heated in the oven and then draped over my dustbin to get the curve in two directions. Have a look, there must be a photo of it in one of the galleries.