Hm. I was interpreting the comment as being that a non-momentary perdo effect (such as, say, a Circle/Ring) doesn't do anything to a target that isn't inside the range of its original effect - at best, it only cancels out spells that are in the circle ring at the time of casting.
However, I was under the impression that circle/rings didn't work that way - that they continued to affect anything (ie, basically pulsed once a turn) on anything that moves within its boarders, until the ring was broken. It lounds like Toa is saying that is not the case. Toa, if I have interpreted you correctly, can you give a reference for that?