The number plate is still attached to the car and thus the shape of the rest of the car affects how air moves over it.
How much is hard to say. Aerodynamics is just hard but basically as the car moves through air it pushes air out of the way and this air also pushes other air out of the way and thus elements next to each other will effect each other.
How much is hard to say. Aerodynamics is just hard but basically as the car moves through air it pushes air out of the way and this air also pushes other air out of the way and thus elements next to each other will effect each other.