Rear skid plates are no good if you have a real bumpy track or a real bumpy whoop section. The skid plate will hit the ground and cause it to no longer track straight.
Im curious,
What's a few mm anyway? I can't imagine this addition of a skid plate would play this much of a factor in the handling of the car, despite what part of the track your on or current conditions.
Wouldn't one prefer the protection?