Based on the pic, the bottom (bumper) grille looks like it has a more direct flow to the radiator than the one on top..correct me if I'm wrong though.
Id block off the fog lamp openings too
yeah you could put in some sort of sheet material to funnel the air towards the radiator. same concept as radiator cooling plates
http://www.aprperformance.com/index....=105&Itemid=52