hard rubber vs metal (tenor)

Since a metal mpc is narrower than its hard rubber counterpart, the embouchure is a bit smaller. Would it be easier to have your embouchure muscles stable on a rubber mpc than a metal one? (similar to a soprano vs a tenor) I try to practice my long tones daily, but sometimes its just not possible for 2-3 days. And I'm often astonished how fast my embouchure dissolves. I hope you people understand what I mean, since english is not my mother tongue.