Just a couple of things I feel compelled to write. The aperture tends to be smaller on higher notes; however, the air will also affect how large the aperture is. In my examples above, I was playing mezzo-forte or softer. The size of the aperture is going to be affected by air and shape. The shape of the jaw’s position, the tongue’s position, facial muscles, and the aperture corners will vary as the note changes. Our mantra is the lips interact with air as if they were the vocal cords.