I cut the wheel wells to the exact scale spec. No overcutting needed. In fact, the foam bumper is an EXACT fit against the back of the body air-dam. Putting the air-dam snug against the foam, and even with the bottom edge, puts the wheel wells in the perfect spot, fore and aft.
Here is a photo that shows how perfectly the front bumper lines up with the air-dam. The ride height is now set at about 5mm. No tire rub at all.