Hi Jutta,

Can you elaborate further about what you mean “the lips slide over the mouthpiece cup”? You don’t mean the rim of the mouthpiece (mouthpiece winds up inside your mouth).

You mean your lips come out of the cup when you engage the aperture corners?

If that’s what you mean, I’m not sure that would make sense as the engagement of the aperture “corners” is a forward motion inwards towards the air column / center of the mouthpiece. I don’t understand how the lips could move out of the cup if you are contracting the corners.

I was just warming up right now thinking about your post and will think about it further.

If you can elaborate a little more, I / others may be able to help.

Best,

John