The flaps arent really for aerodynamics, the airspeed naturally keeps the bra flat if fitted correctly but they do help. their main job is to act as a bug deflector...you see, keeps the bugs off the front and off the screen too, its what they were originally designed for 'bugbra's' then they became a natural protection solution and got nicknamed car bras. the gap between them is an air channel to stop it causing stress on the bonnet at speed with the deflectors channelling the air up over the screen and not onto it