My question boils down to: If you aren't using TWF, what determines which hand is your off hand?
Specifically, I'm looking at Shielded Gauntlet Mastery. It allows you to keep the shield bonus when attacking with your gauntlet, but does not remove the requirement that you have to start your turn with the gauntlet in/on your off hand. Now, we all understand which hand that means when you TWF, but if you aren't what does that mean exactly?
Is it whichever hand is not attacking? Then would it switch with every attack if I use different hands for my iterative attacks? Would this mean that i could make most of my iteratives with the gauntlet as long as I make the final attack with the other hand so that I'll start my next round with the gauntlet in the off hand?
Or perhaps I have to declare it. Does that declaration last the whole round, or can I change which hand is my off hand before/after attacks? Even if it's set for the whole round, then I could still use my "off hand" gauntlet to make all my iteratives just with 1/2 STR bonus right?
Or maybe I'm missing something simple about off hands. Seems to me that it's not well-defined outside of TWF.