As others have mentioned, every board type has a specific geometry. Directional boards will have a sidecut of which the most narrow point will be centered around the reference stance on the board. Yes, even ICS boards have reference stance points.
I don't know all of the technical engineering details, but the best way I can describe the feel of a centered stance on a directional board... it feels like you are riding switch when you are riding normal. That means it will actually ride better switch.
Centering yourself on a directional twin nets the same results due to sidecut. Basically put, when you center your stance on a board that is built with a setback, you are mounting your bindings forward. That's not a good idea.
To the OP: yes, start from reference stance and widen your stance evenly. You can move both bindings back for powder riding. Even if you move just the front foot forward, the ride will be affected. You can move just the back foot back, but it will still handle different. The difference just won't be as drastic as moving anything forward from reference.
I'm also not just pulling this from thin air. I have a directional board and I experimented with every stance imaginable.