Here’s a video by Greg. https://mysterytomastery.com/what-size-mouthpiece-should-i-use/
You will learn that mouthpieces are used to for changes in timbre. Mouthpiece size is a personal preference for the style of music and what is comfortable. It can be like shoe size. Wouldn’t it be crazy if someone asked the question, “What size shoe should I wear to play sports?” If it were a sport that required running on different surfaces I would choose a shoe that fits the conditions of the field, such as wet, dry, artificial, mud, etc. Kinda like that with music. For me, I love the 3C and I also have a 3E, a shallower cup that makes my tone bright. I’m just playing for the fun and memories so I’m satisfied with the 3C. It is easier and more comfortable than a 7C, but I have changed a lot of the way I play (thanks to Greg) since making the switch, so I’m sure I’d play better on the 7C than I used to. The sound of me playing on the 3C is more pleasing to me. Notice I did not say the 3C sounds better than the 7C, this may not be true for everyone. It’s my lips, mouth, air and technique, not anybody else.

I’m just starting the course. Loving it so far, thanks Greg. I have been a 1.5C player for quite as will now. I play a lot of jazz and like the warm sound. I would also like to play lead however never been able to do it on a the shallower mouthpieces because I bottom out and get a double buzz thing happening. My question is, can I do the course on both the 1.5c and the Shilke 14a4a or should I stick to a mouthpiece which is middle of the road ie 3c.:)