To perform this pose, they rest on their legs while positioned wide apart, as if they were straddling an invisible horse. (while those legs are positioned)
After I saw that sentence above, I started wondering the way that "while" was used. As far as I know, if you want to reduce the "while part" of a sentence, subjects of the clauses must be the same (subject of the main clause,and subject of the while clause). But here they are different, one subject is "they"(talking about models) the other is "legs". I think we need comma here because it is unclear that who or what is positioned.
Another question: Don't we need "being" before "positioned" here? As in:
To perform this pose, they rest on their legs, while being positioned wide apart, as if they were straddling an invisible horse.
I have written some examples to understand the issue better. Which versions of the examples are grammatically correct?
1- You can read the new issue of my journal when it is published. (it refers to the "new issue of the journal")
1a- You can read the new issue of my journal, when published.
1b- You can read the new issue of my journal when published.
2- I touched the meat while it was being heated in the pan. (it refers to "the meat")
2a- I touched the meat, while being heated in the pan.
2b- I touched the meat while being heated in the pan.
3- You can use my computer if it is available. (it refers to "the computer")
3a- You can use my computer, if available.
3b- You can use my computer if available.