Actually, I think I was incorrect. Greg mentions that the tongue is not necessary to change pitch, only the aperture corners; the tongue arch effects the resonance of the sound but doesn’t determine pitch. I think basically the tongue is secondary to the aperture corners tightening–without the tightening of the aperture, arching the tongue would not change pitch on its own. Hope that helps / makes sense, etc.

BTW–I am definitely getting that sensation doing the harmonic slur challenge, especially at softer volume.