[diesel_john]

agree with Frank the low pressure areas are the hardest to control
first pic
shallower windshield just doesn't require as big of a hump on top to stay laminar

if by changing the windshield angle if we can help fix what's on back more easily or more economically then it's worth it.

my question always seems to boil down the same, should we steer the majority of the air from the front over the top or around the sides?
one or the other is much easier than both.

second pic concept of a thin wall built on top edge the length of the car would direct and hold air over the top of the car. a sort of tail gate up variation, air would fill up the space in front of the windshield and flow over the top at a much flatter angle, in theory, of course.
intuitively it looks like no way would it reduce drag, which may mean that no one has ever tried it.