I have a Yani soprano S902, the stock mouthpiece (an HR5) won't go down much past the halfway point even with lots of lube. I have a Bari Esprit which goes on no problem. The bores are: Yani 13.52mm, Esprit 13.75mm.
It's easier for me to play quietly on the Yani right now which is good for practice at home, but I hate to sand down the cork if it's going to make it hard to use other mouthpieces.
The cork is a bit discolored--am I having problems because the cork has lost its elasticity, or is the Yani unusually narrow (seems unlikely), or?