As I understand it, a freestyle target can be taken prone or seated, and the shooter has the choice. Most of us choose seated, but we could opt for prone if we felt it brought some advantage. The fact that we don't, suggests that there isn't any advantage.
Would it be possible to have a choice of position for standers for all shooters and not just those with mobility issues? Then, the able-bodied could either stand, or take the shot in the "disabled standers" position if they felt it brought some advantage.
Edit- I was typing this while Scooby was posting.........