Surface traction as rbe3. Momentum?

If it’s flat, do you think the moment could be applied to the top of the gasket (flat) instead of the inner section (Curved)?

I have posted a check file which shares some points in common with yours using couplings on the Mecway forum and agreement is nice according to theory.
It’s a pipe section under torsion.

Hello,
I cant use that surface to apply the coupling. So I dont know really how solve this issue.

This constrains are used to simplify more complex interactions.
If you don’t find any other option, I would include in the model the agent of that moment.

¿What is generating that moment that you want to distribute?