I think the wheel gap is related to drag. You would think a smaller gap equals less drag, but that might not neccesarily be so. Maybe a larger wheel gap releases air from under the car?
On the ZO6, look at the area just behind the front wheel, it is carved out in that area for less drag. Its got one of the lowest drag coefficients.
Just my s.w.a.g.! (scientific wild-ass guess)