FWIW, I think it is a good idea to practice with a progressively "growing horn setup." Let me explain.
Start out horse flapping, ala Shew.
Next work on some lip buzzing exercises (no mouthpiece or rim).
Now buzz some exercises on a mouthpiece visualizer. I had one made from a Bach 1&1/4 C rim.
Next would be a berp routine.
Insert the mouthpiece into the lead pipe now and have at it.
Finally put the mouthpiece into the complete horn.
Each new step will add to the resonant partials available. I feel that practicing this way can really help you develop the "driver" of your horn, your chops.
I have been doing this quite a bit for the last six months and have added a fifth to my range in practice and rendered the brutal rock and show jobbing gigs much easier to deal with.
In short, it works for ME. Whether or not it is of any use to anyone else can only be determined by that individual.
Just a thought.