the ducts should be pointed directly at the back side cnter of the rotor. I agree with DSC.
there are some ducting kits for BMW that are pretty trick:
M3 Competition Brake Duct Kit
As used on our IMSA cars
A custom made front brake backing plate with sealing lip that precisely fits the inside of the brake rotor. Air is brought in from the front spoiler under pressure and forced into the center of the rotor and out through the vent holes. Provides superior cooling under hard use. Kit includes special brake ducts (install in fog lamp openings), 6 feet of brake duct hose, backing plates with 2.5" hose fitting (3.0" available by request), clamps and instructions. Requires R & R of wheel hubs for installation.
P/N 3451M3RACEK
