All of the mules have it on the trunk. If the plate were going on the bumper that would mean that they were using a different trunk lid and seeing how it might affect the aerodynamics of the car, they would need to do some real world testing with it. Given that we haven't seen any mules with either a plate on the bumper or a taped up trunk. I'm guessing that the plate is going on the trunk. I also think it looks better, although that is completely personal preference.