Feel dumb asking this, but am putting it out here anyway. All things being more or less equal, to play higher one needs a smaller aperture and greater air pressure, right? As a dedicated retread of 3 years who practices intelligently every day, my range is s-l-o-w-l-y creeping up, but is still not at high C yet. I did a self-check the other day and noticed that beyond an A above the staff, I can't seem to increase the air pressure in order to play higher. My chops seem/feel fine, I'm not choking off the air at the throat nor using excess mouthpiece pressure, and my sound is solid enough within & below the staff, and both good and fairly effortless up to the G just below that A. I generally play a Schilke 14, which is not overly large. So how does one increase air pressure in order to play up there?