This video makes a good point. I have had a student mask a car like this before. The buildup of coatings on the plastic starting flaking off onto the paint when the spray gun pressure hit it. The plastic didn’t actually flap over into that paint as described in this video. However, it did make a mess with the flakes of paint landing in the fresh paint job. Fortunately, he was painting is jambs and that is where the flakes landed. We were able to buff it out without having to repaint the surface. Be sure to follow this tip, as this could cause you grief and may result in a repainting the surface.
The correct way to perform this is to outline the area that you are masking with masking tape and masking paper then simply tape the plastic to the paper. Allow a minimum of 8 to 10 inches of paper before applying the plastic. This is a quick masking tip that will save you from additional work.