I agree with Al's comments. Once I've played my G on top of the top line of the staff, I feel I've entered "upper register" territory with the A. My lips are in the "high C" mode, as the A is first and second valves and the high C is open, then it's up to high G, then it's a double A. (Like I've got to worry what to call a double A as if I could play it!!) Oh Great Double C, where are you??????