At what speed do you have to have a window net?
I've run into that a couple times. My local track wants me to use it all the time but like I said to them I have a cage for my safety not because I have to have it. When I use the nitrous they will know becasue the window net will be in the car. They decided that was ok. Other tracks never even brought it up..
Some tracks require net on any car with cage, even if running 16's. Might be worth a call to your local tracks.