just want to make 2 observations, nothing scientific necessarily.
1. 2 people of similar height, say 6.2. one guy has a shoulder span of say, 2 feet. the other guy, 3 feet.
if they are going to have a stance width that corresponds to their shoulder width, one will stand 2 feet apart, the other one 3 feet apart.
so this saying to stand apart about shoulder width probably needs to be interpreted a bit loosely, particularly if the above 2 gents have similar swings. i would think the similar swing, on a base that is one foot different in length, may produce vastly different outcome.
2. everyone has a difference sense and level of balance, esp dynamically. if a "natural" stance produces an acceptable swing, i say leave it to be, at 2 feet or 3 feet, whatever the case may be.