Maybe they (the wing openings) help keep the back window clear in heavy deluges, or help clean grime from it when it rains at all??
Do you have access to a wind tunnel, or are you just running an industrial fan in front of the car, using smoke/vapor mist, and taking readings that way?
Do you have access to a wind tunnel, or are you just running an industrial fan in front of the car, using smoke/vapor mist, and taking readings that way?