Hold your helmet up against the inside of the front and rear (main hoop) funny car cage bars. Hold a straight edge across the outside of the bars. If your helmet can touch the straight edge at any point you try between the bars, they may want the net to extend back to the main hoop. Or you can add/re-position tubing to keep the helmet completely inside the cage.
Typical net in that application is attached to the door bar at the bottom with a bracket and small screws and at the top with seat belt style buckles on the front and rear of the net. Release the buckles and the net falls down completely out of the way. It's going to be a custom deal.