Hey there! I'm not exactly sure on what you are pertaining to but I've posted an image below showing priorities. The priorities count clockwise but the lowest priority is NOT in the back so it should be S. You can watch the set of videos for this topic here if you haven't yet: https://www.clutchprep.com/organic-chemistry/the-r-and-s-naming-system/?c_id=14727
I hope this helps!
Thank you it did!