I'm going to put in my thoughts based on no scientific evidence whatsoever too. The air pressure over the bonnet would be affected by the shape and angle of the front bumper, something wedge shaped would put high pressure over the bonnet as less turbulent air, maybe why few gains/losses on rx-7s. But a flat fronted something would cause a lot of turbulence and a lower air pressure flowing over the bonnet than that of a wedge shaped car, maybe allowing bonnet vents to be beneficial if placed properly. But I don't actually know anything, I'm jus guessing and want to feel involved.