That is the principal. Reduce the entry space to strip away the volume of available air pulled around the wheel/tire. Use the spat to cut away the high pressure air flow into the face of the tire. That high pressure point is really dense air, and acts like a brake against that surface.
This will only be incremental gain, because we have really dirty air flowing around these bikes.
That means, in other words, "...make lots of horsepower!"
JimL