the sling can be used in any of the shooting positions.
What you describe is difficult for me to imagine and I'd rather see it in the flesh.
My suggestion is that you ask people at the shoot for their views on the plinking range.
If you do fancy extending your experience of FT then I'd suggest that you practise the seated position. This is because although prone is a legal position in FT there is no stipulation that the targets need to be viewed from the prone position hence you'll likely find your view obscured or find plenty of grass in your scope picture.
Good luck with your venture