On my 9"5 I have set the straps with the widest possible stance, it feels much better in the surf that way, whatever the size or type of wave I'm on.
Fin all the way to the front of the box, so that my back foot is just over it, I find the board easier to turn that way so far, I would only put it back in the middle of the box in bigger waves, but that is rare where I am. That's still something where I need to experiment.
I used to put the mast foot all the way to the back, and it works fine in tiny waves and when you're planning all the time. But when I'm shlogging to go outside of the break or/and the waves are bigger (from waist high and up) I feel better with the mastfoot between a third of the box and the middle of it.
In general, the lighter the wind, and/or the bigger the wave, the more forward I set the mastfoot. But I don't think I would go further than the middle of the box.
The MT is a different shape , but I'm sure I would apply some of these rules as well if I were on it.