The idea of what a peashooter mouthpiece is dependent on several factors.
1. The size of the players lips
2. The muscle strength of the players embouchure
3. The actual embouchure type used. (This means lip curl, lip pucker, as these things require different amounts of cup room to do the same job.)
4. The resistance between the players embouchure and his trumpet. ( If I play my old .472 bore NYC Callet I can use a Schilke 14A4a, or a Jet-tone (Roman) mouthpiece. If I play on a horn with more resistance like a Bach 37 Ihave to use a more open mouthpiece. LIke a Schilke 14 with a bored out throat. )
There was a question about mouthpiece depth and range. It is more a factor of endurance than range. It has to do with acoustical load. The lips buzz as they try to resist the air stream. With no mouthpiece they buzz without the aid of feedback (impeadance) from the mouthpiece. A mouthpiece with a large cup VOLUME ( a variable of diameter, depth and cup conture ) gives less feedback to the lips than a mouthpiece with a small cup volume. However this is usually offset by slight embouchure changes. If I play the Stevens with no pucker then my lips do not protrude into the mouthpiece and I need a smaller cup volume. If however I employ a lip pucker (& I do sometimes) then my lips do go into the cup and make the useable amount of cup volume less. Afterall the space that my lips occupy is no longer useable cup space. In this case I need a mouthpiece with more cup volume.
Cup volume is a measurement of how much water the cup of the mouthpiece can hold. They used to close off the throat and fill the cups with water to determine the total cup volume.
There are too many variables for anyone (who has not heard you play or know how you use your embouchure) to tell you what is or is not a good mouthpiece for you. You would get the same results by throwing darts (while blindfolded ) at a mouthpiece chart and using the one that you hit.
A collection of some past posts & information about