Copying channels and mix assignments in editor

I’m somewhat confused about what is supposed to happen when copying channels and mix assignments. Copying channels seems to copy (almost) everything except the mix assignments, and copying mix assignments seems to copy the mix assignments, but DOESN’T copy the pre-post fade settings? Is that how it is supposed to work? I was expecting it to copy the pre-post settings as well. Haven’t had a chance to check on the real desk yet to see what happens there. Is there a way to copy the mix assignemts AND pre-post settings?
Context was moving an aux to a lower numbered aux so I could free up some mix resources to assign a stereo aux. I just wanted to make an exact copy of aux 7 to aux 3.