I think you're missing the boat on where the air is actually coming through the plate.... It isn't coming through the round hole.
Originally Posted by The HACK
The opening of the backing plate should point to the hub area of the rotor, not the rotor itself to provide maximum cooling effect. By directing air straight at the rotor, two things will limit the actual cooling capacity. 1) At speed the rotor will be spinning rapidly creating a high pressure area around the surface of the rotor in which the plates are directing air to, reducing the actual cool ambient air reaching the surface of the rotor and 2) even if it does effectively provide air to the rotor surface, it can potentially create an uneven cooling effect between the inside facing surface and the outside facing surface.
The reason why the air should be directed toward the inside of the hub, is so the internal vanes can draw the cool air out much more effectively while spinning, thus providing better cooling effect and also cool the rotor consistently. IMO that opening should be moved down to cover 1/2 of the hub opening.