Have you done any testing to measure air pressure (or air flow) behind the intercooler? Or have you measured IATs and are basing your decision on that?Someone before me had, but I actually closed them off again to lower air pressure behind the grille and increase it in front. In other words, the grille opening only feeds the shrouding. Same thing with the smaller grilles below the bumper, I closed it off to decrease turbulence and pressure in the area in front of the intercooler, so the cavity fills from the air entering through the grille.
Pressure differential is what gets air moving.