I started learning (a silver) flute some decades ago, and can now play just enough to keep myself amused, but I have a way of explaining the difference between playing the lower octave, and the higher one.

Imagine you are talking at normal volume to a friend, and suddenly see another friend across the room or along the hall. If you shout across the room, not yelling loudly, but loudly enough for your other friend to hear you, how does your breathing change, and how does the way you shout differ from the way you talk to the person standing next to you? It seems to me that the "Hey, we're over here!" shout is the type of physiological process which makes it easier to do the higher notes on the flute.

You might find that being aware of that difference helps you to be more aware of how you play the higher notes.

I used to be a class teacher too, so it's the difference between talking to one student to explain something, interspersed with "Johnny, sit back down and I'll come over there and talk to you next".

Helen