Al talks about that issue in his book Pushing The Limits! Basically feet together body straight is the ideal, but it’s so difficult and cumbersome that I can’t even recall seeing a completely perfect rep anywhere. Although Al and Jim Bathurst from beastskills.com (one of the models for CC) have put up vids of very good attempts, probably the best I’ve seen.
But in the real world, since you practically have to twist your body so much when your feet are together, it’s better to spread your legs. But, this should be minimal, I would shoulder width or less is ideal, but no more than 1.5x shoulder width. And with this modification you should be able to keep your body pretty straight and level. If you need to twist and lean a whole lot and spread your legs super far then you probably should just do an easier exercise instead.