I did a tuft test of my Civic, which has them too. They are even more pronounced on my car, and I thought for sure that they channeled air over the car.
Much to my surprise, the air smacks right into them and keeps on going towards the sides of the car.
They certainly do not help channel air over the roof as I thought.
I had a really good straight on shot of this effect .... but I deleted it ( smack ! )