It's my observation that when the screen is all the way up, the air just spills around the sides instead of going over the top of the screen. Air, like water & electricity, seeks the path of least resistance.
If a committed user wanted to play around with aerodynamics, it would make sense to add vertical "winglets" to the screen to create a channel which would direct a more-coherent stream of air over the rider's head. Just a thought...
When they say Harleys are for 1%ers, I don't think they mean guys who sell crank and get in bar fights any more.