One of the big proponents of the squared up stance was the HK International Training Division. When I worked there that was the stance taught to control the tendency for full auto fire to climb high right (the path of least resistance on right handed shooters). It was described as feet, knees, hips, shoulders square to the target, with slight knee bend and forward weight transfer, IE: if you dropped a plum bomb from your chin it would hang in front of your knees. The toes of the strong side foot are about even with the heel of the support side foot and feet are about shoulder width apart.

It works well with a subgun, but for heavier recoiling weapons most shooters find it more efficient to open their stance, placing their support side foot further forward then the strong side foot. This change in foot position results in a more bladed stance.

I like a relatively squared up stance as it allow me better ability to move and traverse multiple targets. Having said that you do not want to be in a Sponge Bob stance (copyright LAV) with everything straight and square to the target standing upright as this will provide no recoil control.

The reality is that once the bullets start flying you won't be thinking about foot position. As long as your upper body is in an aggressive weight forward position you're on the right track.