in my opinion what you have done is ugly, i hate people that do that (nothing against you though).
now your idea is right but what i would do is run the ducting into the bar next to the number plate. do you see in your third photo the bar and plate how there is the gap? well have the ducting run there
that way it is not visible and cops cant say a thing, hell they wont even notice its there AND the air flow will be exactly the same as where you have it now.