I don't see it mentioned; but be aware of EAR FATIGUE.
Too much time listening closely to Anything can make it all start sounding the same.
If you find this true and things get Confusing...
TAKE A BREAK.
I experience this. If I'm mixing for a while (I use headphones) I keep turning it up. And by the end it's like getting cranked. But lately I've learned to start with it a lot lower and it still seems loud right off the bat. LOL. Your ears get used to the volume and then it sounds quiet.
First the vocals were too deep in because I was concerned that it would sound dumb if they were too much on top. I tried to fine tune it a in the mastering with a little eq in the mids were the vocals are prominent.
so, the mix is where the fixes happen and the master is only final total product polish, right?
In short... yes.
However, this brings up another point about mixing. "Fixing it in the mix" is a terrible mindset to approach recording from. It is imperative to get it right during the recording. You never want to pass along shortcomings (on purpose) to the next stage of the project believing they can "fix it".
For years I used to have a little sign in my project studio to remind me.... "fix it in the take, not in the mix". That sign is now gone, but the philosophy is deeply embedded.