The engineered formula for finding the optimal protrusion of the exhaust exit is as follows:
Stand at the right rear corner of the vehicle, perpendicular to and on the same axis as the panel from where the exhaust exits. Put your head down so you chin touches your chest. Walk forward until the crown of your head contacts the vehicle. You should be able to see approximately 25mm of the tip protruding from the horizon of the side panel. A tolerance of +/- 13mm is acceptable.
Be sure you have an audience when you perform these calculated measures.