I did a little CFD work in a amateur grade program on your car, but still came up with some interesting results when i blocked the bumper 'pocket' on one side and left the other stock.
Apparently, there
is some 'aircurtain' effect going on. ( Note the pressure difference in the front of the tire on the unblocked side.
On a side note, i got the approximate Cd down to .28 by blocking the upper grille flush and closing off 3/4 of the bottom.
This is the stock side :
And this is the blocked side :
There is more stagnant air on the blocked side ( the dark blue )