This again, is partly what I mean by framing your points using your own anecdotal experiences as evidence. For me to respond to your thoughts here I suggests that I feel you're teaching wrong. Let's try to remove our personal stories from this conversation and discuss this a little more dispassionately. I'm not opposed to hearing about different pedagogical approaches and discussing their merits, but talking about your personal results makes this impossible without this topic turning into a flame war.To resolve this in my tutoring beginners, I use a very thin coffee stirring straw that can pass through a mpc to center their mpc between their lips, This seemingly negates my concern about whether their lips are thick or thin. The results speak for themselves in the sound produced.
I agree with you that these are important points to consider, but you leave off what you think should be correct. Where do you feel the air stream to go after it passes the lips?Think of it this way if you will. Consider your aperture in relation to the throat of your mpc. Then is your air flow sliding down the sides of your mpc cup and centering into the throat or fanning out either upward or downward and partially dissipating?
Frankly speaking, I don't think the real issue in this topic is whether or not it's fine for some players to place their mouthpiece on the red of their upper lip. The basic situation we're discussing is a particular embouchure type that most players and teachers are completely ignorant about. Honestly, I don't think many players and teachers seem to be knowledgable about even the more common embouchure types. The actual matter has to do with the tradition of how we teach embouchure. It's fashionable to dismiss and deflect questions about the embouchure and focus instead on breathing or practicing specific exercises. Yes, this can work very well and I'm not advocating we throw the baby out with the bathwater. However, the willful unfamiliarity us teachers sometimes demonstrate regarding embouchure form and function only serves to perpetuate a culture of ignorance. If the only tool you have in your toolbox is a hammer, every problem begins to look like a nail.