I've heard that some of the air that flows over the windshield is also "squished" towards the edges of the A-pillars. The "squished" air is then met by the air that is travelling along the side of the car, and then creates a vortex along the sides of the roof. The image I have in mind is an airplane taking off from a dusty runway and generating a vortex at the ends of its wings. (Picture a long curl/corkscrew being dragged through the air from the upper right and left of the windshield.)
Still with me?
OK, for those who are here's my thought: What if I added relatively small fins that run from the bottom of the A-pillar all the way to where the roof "begins"? Shouldn't this improve the way the air would flow over the car, reduce turbulence, thus improving mileage?
I'd also imagine that this would reduce wind noise, but that is speculation.
Any thoughts?