Sticking my oar in as a “needs help” rather than a “has help”….
I’ve just picked up the alto again after several months of playing only tenor. My middle register isn’t quite such a disaster area as it was before, but it’s still pretty bad. The C and D are very unstable, and everying above A is prone to a kind of rushing, whispering sound. Pinching helps but doesn’t completely fix it.
It might be partly psychological (unpleasant high-pitched sounds make me flinch) and the instrument itself is maybe not the best. Still, I’m definitely doing something wrong. The middle register on my tenor is so much easier!