Airflow at front plate
 

I searched for tuft tests, tunnel tests on here and on Google, without much luck.

Looking for how the air flows around the front plate. The reason I'm asking is I'm thinking about using one of my spare 80"s gm flip down plate holders in the front. If you flip this around, the closing spring will hold the plate cracked slightly open (opening at bottom). My opening in the grill block is directly behind this area currently. The idea is to use the air pressure at higher speeds to push the plate back, and closing the gap. If the air moves upwards more than it pushes back or to the side/bottom, then this won't work. This will be on my civic vx . Anyone have any thoughts, or just try it?

pressure
 

If you'll check out Motor Trend's article on VW's Jetta hybrid land speed record at Bonneville,you'll notice that at 187-mph,the stagnation pressure is only 1/2 psi higher than at 70-mph.
I don't know if 'normal' highway velocities are going to be of help.
Even at 420-mph we're only looking at around 4-psi.