I would worry that "moving the circle around" is too broadly defining how circles/rings work, and would lead to "abuse" - but ysmv.
What you do have to be careful of, you can't (in Hermetic magic) have an effect that then itself casts a spell. So a Hermetic Mage can't create an effect that then allows anyone later coming in "range" of that effect to gain an effect.
o Good Example: Circle of Night Vision:
Gives Cat's Eyes to anyone within the circle when the spell is cast.
o Flawed Example: Circle of the Gift of Night Vision
Gives Cat's Eyes to anyone who enters the circle while the effect lasts.
The mage casts the effect - the effect itself doesn't cast an effect later. (exception: Watching Wards, some rare legacy spells, etc.) Of course, you can houserule anything you want - just make sure the rule is consistent and not open to (whatever you see as) "abuse", and you're good to go.