Breathing through the corners. Reinhardt is very clear that the vibrating points of the lips remain in light contact throughout the inhalation. What I feel, and watching in the mirror with a rim confirms it, is that two situations seem possible:
1) I make a conscious effort to maintain contact in the center of the vibrating aperture during the inhalation, which in practice seems to coincide with the tip of the tongue refusing to leave the roof of the mouth just behind the upper front teeth, in which case it's restricting air intake somewhat
or B) Maintaining mouthpiece pressure, but not 'actively trying' to maintain central lip contact, the tongue naturally moves back slightly into something like the "IM" position Reinhardt describes and more air is taken in for the same effort ... but the lips are no longer touching at the very center. They're not moving under the rim, and they're still just touching in the outer 1/3rds of the area within the rim, but they do part very slightly in the center. Not enough to be inadvertently sucking air in through the horn or anything like that, but not 'officially' touching either. But then the centers naturally return to real contact as soon as the mouthcorners snap back into position. So is that Good Enough? Following this version of events with air attacks seems fine and suggests that everything ends up back where it started.
(Same thing applies to the Buzzing Routine inhalations if I try to do it without the finger - I can maintain 'L&R central contact' roughly where the inside edge of the rim would land but not necessarily perfect contact right in the middle.)
Apologies for length - I'm trying to form new habits, so some overthinking probably comes with the territory
