NFHS - yes, ref from the floor if there’s no proper stand. No guidance for moving back and forth or not
AFAIK. As a floor R1 I tend to start on the receiving side (as they’ll have the first attack) and stay there for the duration of the rally. And move back and forth as R2 as usual.
NCAA - Stand is required.
3C2A - No idea, but I’ve worked from the floor on a couple of occasions.