I find most embouchure discussions to be of little use because: 1) we have never worked with or even seen the player 2) if we had, we would have discovered that they probably didn't have real trouble with the chops, rather only a symptom of miserable body use and breathing as well as some really weak practice habits. I often get the impression that players throw the word "embouchure" around like the words "love" and "hate". When they do, others jump in with advice that would be fine if there was a magic geometry called "optimum embouchure". There isn't. Anyone with good endurance got there by getting the basics down, a bit of luck and THEN perhaps some fine tuning. The basics are far more critical than the geometry. My take is, get your breathing and body use act together before messing around with geometry. The chances for improvement are FAR greater. A moving chin shows some weak basics. My recipe would be long tones and slurs with no tongue attacks. Inhale and exhale, then replace exhale with play - NO TONGUE. Once that works, do lip slurs the same way - exhaled through the horn. Once you have a solid sound with air only, only a small amount of tongue is added - just enough for articulation.