I’m finding this a really enlightening discussion.
I know we ought to be able to figure out how to do this without visual aids (after all, great trumpet players have been doing this for centuries now), but wouldn’t it be great if someone could produce a mouthpiece with an endoscope built into it optimised to give a view of the aperture as we actually play? Looking around on the web today I can see some quite cheap ($40 – $50) endoscopes that attach to a mobile phone to allow for viewing/recording of video, but unfortunately all seem to have a minimal focal length of around 2 cm. It would almost be worth getting a hole drilled through an old mouthpiece the size of the endoscope (somewhere between 5.5mm and 8mm diameter in most cases) to experiment with this, but I suspect that with a 2 cm focal length for the endoscope camera, the result would be out of focus, and I’m not sure one would get a wide enough angle to see the whole aperture in action anyway. Sure would love to see what’s REALLY going on when I play, though.