[Christ]

A bubble in this sense is a high pressure area which will resist inflow. Since the pressure at the base of the windshield remains fairly constant, we can identify that it's working to this effect, meaning that, in some respects, it is acting as though a dam of solid construction were actually in place. Pressure, however, cannot be maintained outside of a container without some transfer of energy. Because of this, there should be a gain to be had at the base of the windshield, as long as there was a bubble there in the first place. The size and pressure of the bubble determine the actual scale of improvement.