When people say the snooker stance is more "square" they are only talking about the hips & feet. The shoulders end up in a similar position to the side-saddle pool stance. Left shoulder is low & near jaw. Right shoulder is higher & behind right ear.
This rotation is what results in the full body constraint that snooker players enjoy. The spine rotates from the squared hips to rotated shoulders (relative to the shot line) which places it in tension & makes it less prone to movement.
The hips are locked by the position of the feet.
The shoulders are locked by the tension in the spine.
The only body part that is free to move is the cueing arm.
When you feel this sensation, you will be committed to the snooker stance.
Further, the stance (when done correctly) places the right foot, bridge hand, dominant eye, right shoulder, elbow, & grip hand in alignment. You might even feel like your body is pressed up against a wall (a single plane). Think about how important that is.