you are right, there are many parts that dont work with a sealed brownie pan but its more accurate than a cup and thought it would give a better idea of the water forcing the air out as it moved. to be realistec if you cut a slit in each side of the pan to allow for the same air release as a car hood then we would be talking apple to apples. plus the idea of a pocket of air is a reality for only a short moment. The pressure of the water pushing up into the pocket would force the air out through those cracks at the top of the radiator and fenders the same way it would as if your cup or pan had a hole at the top.