I recently tried a bunch of different mouthpieces and found one that seems to fit me and my horn.

I then had a friend work with it. We did a paper test on it to see if it would sound better if it was not inserted as deeply. After confirming that it did sound better, we started some modifications.

He added an inside and outside bevel to the shank. That did not seem to do too much.

Then we slowly filed it down trying it after each filing. Now I am hearing more overtones and a good mouthpiece seems to be even better. Db3-B2 which did not slot before is now slotting.

Is anyone else experimenting with mouthpiece insertion depth or modifying mouthpiece shanks with bevels?

Just fyi the mouthpiece is a Bach Corp. 11c in a Yamaha 891z.

I just use Teflon tape, but all that stuff is just a compromise. I've found that the best mouthpieces go in a bit further, but are also longer overall.

The exception is the Alessi piece which seems to go in a hair less but it's also shorter overall.

Reeves makes sleeves for trombones now. I’ve been curious but it’s not an inexpensive thing to test and I already use Doug’s interchangeable system which offers a sufficient amount of variety for me. I also tend to swap out my leadpipes for ones I like and all of them seem to work well with a 1” insertion depth.

You said you confirmed it sounded better when not inserted as far, then you started filing it down to make it go in further?

Filing down the end doesn't make it go in further. The top of the mouthpiece shanks hits the same part of the receiver. The bottom part does not go in as far if filed down.