our prophet always said to his companions to stay close and make no gasp between shoulder.... and this is our prophet tell us to do so.

but if we have no gasp between feet that's also sunnah. but the obligation to make no gasp between shoulder is stronger to do than no gasp between feet.

the conclusion is, we have to make no gasp between shoulder, like the prophet said even if our feet seperate from each other. but if you want to do the sunnah, after close shoulder to shoulder, you need to close feet to feet.
that's all i know

salam