I wanted to add something to the above post about keeping the air and chops balanced. Once you get used to playing that upper G with almost the same feeling as a middle G, you will realize just how OPEN your embouchure feels. With all of this new room, the embouchure opening has more room to decrease in size as the air increases in speed and the upper register increases. The same goes for the lower register. If you can play a low G with basically the same "opening" as your middle G, you have much more room to "open up" down there when needed. The key is having control of your air, like a gas pedal on a car. It always needs to be steady and consistent in speed so the chops have a wall of air to resist against. If you ever let the air collapse, the chops will collapse when going up and you will "pinch out" your high notes. In the lower register, if you let the air collapse or the chops too relaxed, you end up being too open and your chops are just flapping around with no center.
I hope this is helpful. Just writing it, I am scratching my head because it is much easier to explain in person.
