Mouthpiece placement and embouchure development is an important subject but one in which a good teacher is very helpful. In playing the Maggio Way the mouthpiece is preferable placed 2/3 on the top lip and the lips are sloppy wet. The lips are closed and the top lip slightly overlaps the bottom lip. I know from my own experience that the top lip holds the mouthpiece in place by gripping it on the outside. The muscles in my top lip outside the mouthpiece are noticeably developed but there is no gripping by the bottom lip which is left free to move up and behind the top lip as I ascend in range. One gets as much of both the top and bottom lip in the mouthpiece as possible by keeping the lips closed and overlapping. The center of vibration inside the mouthpiece must be free to vibrate and the top lip does most of the vibration while the bottom lip's role is to regulate the aperature. I don't detect any muscular development of the top lip inside the mouthpiece. Play the Pedal Tones to set the embochure correctly. When I am practicing, I play the Pedal Tone exercise before every thing I play. The goal is to play everthing throughout the entire range with the Pedal Tone embrochure. The 'Nose Breath' is used whenever necessary to reform the embrochure in the Forward-Closed position. Buzz downwards.
Practicing the Pedal Tones on the mouthpiece alone is extremely helpful in embrochure formation and teaching the lips to vibrate correctly. The trumpet can mask problems that become easily evident on the mouthpiece only.
Get the book 'The Original Louis Maggio System for Brass' by Carlton MacBeth. Buy it at
Music Books, Charles Colin Publ Brass & Jazz Methods, Practice rooms, music lessons
Follow directions carefully. Every word is important.
Basically, I think your teacher is giving you correct advise but there is possibly more to it and this book will help both you and him.
One last thing is that the bottom lip is free to move and I have never noticed any pressure on the bottom lip at all.