Urban, it doesn't matter if the radiator has a direct path to air.
Ok, it does, but it doesn't have to. Pressure is what makes air flow through the radiator. The air will turn if it needs to. If you put a big fan blowing in your bumper right now, you'd see that most of the air entering the bumper exits somewhere other than through the radiator. Everywhere it leaks, put a shield there. If you seal all the holes up, then when air enters it has nowhere to go but through the radiator, and pressure will build up, and then air flows through the radiator. Even if you had good shrouding right now I can see the top of the radiator is wide open, so air would just go over the radiator, and possibly under it.