It seems to me that a lot of players play with way too much upper lip pressure, and could use the lower jaw to take some of that pressure off. I like to anchor on the lower lip/jaw (I think of this as one unit, ala Reinhardt) and have 60% of the pressure on the lower lip and 40% upper lip. I like to set the lower lip/jaw anchor first. During my set up/warm up phase I'm aware of the mouthpiece against the lower lip but don't really think about it much after that, unless I'm tired. By rocking the mouthpiece off the upper lip and a bit more onto the lower jaw/lip I can get a little more endurance. I also think of a triangle from the corners to the lower jaw, and I notice some firmness there. But in the heat of battle, I just take a breath and play! However you do it, don't dig into the upper lip. It does most of the vibrating!!