The short answer is most people are not going to have the same range in the beginning because you are learning a new way of playing. I know you are waiting on Greg’s reply, but here is my experience.
Just like you, I changed my approach to playing. One of the things I would do to play higher was to pinch the lips, constrict my throat, engage the abdomen and apply more mouthpiece pressure. Doing those things enabled me to play a few high C’s and D’s in a high school band. Those techniques came with a price. I played with pain and often missed the note or fell off high notes above A.
I am now retired and I have picked up the horn for fun. After a couple of years looking for solutions, I stumbled across MTM. When I started training using MTM, I replaced those damaging habits with new habits and new sensations. I became like a beginner in my playing. F at the top of the staff became more challenging to play because I was not going to engage all the inefficient techniques. As I began to learn more about aperture corners, shape changes and sticking with the process, I could play high C with control and without anxiety and pain.
I have only gone through the Moderato and that level has taken me far enough t0 really play for fun. One day I will resubscibe and find out how to do what I thought would never be possible for me. I now know that playing trumpet doesn’t have to hard and painful, thanks to Greg.