Out of curiosity, how are folks handling the use of magic circles for general trickery as opposed to flavor text in thaumaturgical spellcasting? From the novels, the properties of magic circles we've seen include:

1) Completely cutting the area within the circle from outside magical energy.

2) Requires little power to close (Harry routinely calls it a "tiny effort of his will" or the like) and doesn't seem to "scale" with practitioner power; I don't recall any instances of a magical creature or a spell punching through a circle because it was "more powerful."

3) Disrupted by even the smallest of physical breaches: even a stray hair or scuff mark can break a circle, and in Storm Front
Numbers 1 and 2 point away from modeling this as a straight-up spell (for example, in Turn Coat ). Currently I'm thinking it should count as a threshold, but I'm not sure what base strength to set it at.

Thoughts?