I recently replaced my Windvest windshield on my 2012 fatboy with a Harley 21" billboard windshield. The Windvest is a minimal coverage windshield and the Harley is a maximum coverage windshield.
This is where the interesting observation comes in. With the Harley shield I notice quite a bit more engine heat on my right thigh. With the Windvest my right thigh didn't get nearly as warm. So it seems the Harley shield is blocking more air circulation to the engine.
Anybody else ever notice this situation?

 

Why do you think harley tried to buy out windvest? Because it was superior to anything they put out.

 

Funny. I ride with and without my full size HD windshield and don't notice any difference in engine heat at all. Even my oil temp gauge reads the same.