I could be wrong, of course, but I don’t think they contradict at all. Greg is just breaking the pieces down and separating them – Jim is combining them.

Greg is trying to get folks to understand the concept that shape can change notes – it’s not a requirement to increase the air kick to ascend – rather you can change the shape (which in turn increases air speed which increases vibration/pitch). If you want the pitch to stay at the same volume, you add air, which essentially keeps your aperture the same size (which requires the use of your corners to “hold” the aperture open).

This is my understanding at least…