Ah, I got up to that platform, but I guess I missed the button. My blue light filter was probably on at the time so I couldn't see it.
The flying feels good, and playing with momentum in the way you are is very interesting although I had a hard time with the last level. I was not holding the dpad down after being flung through the barrier, as that didn't instinctually make any sense to me to gain momentum while not in bird form.
Also, I found a way to cheese some levels by just hammering on the a button. you gradually gain altitude just jumping up a little bit at a time. :D