Great points Ron!

Shape is the formation of the aperture using muscles in our face and tongue level.

We want the engagement of muscles on the outside of the Mouthpiece and keep top lip relaxed as its what vibrates and needs to vibrate fast to achieve a high pitch.

Harmonic slurs help us hone in on efficient Shape change if we diligently don’t use air to kick. Constant, passively released air helped me isolate what Shape consists of. We are all different, so Greg cant tell anyone what precisely/exactly to do.

But, generally speaking, the bottom line is that we want to gradually (slightly) reduce the size of the aperture as we ascend without engaging the vibrating surface directly or over tightening / closing off the air.

Resonance is optimal efficiency and is the optimal Balance of Shape, and Air.

Good luck, hope this helps FWIW.