Good answers all, thanks for the foof for thought.
Moving on to another couple of questions.
Regarding Morgan's Earth Stomp spell on YS293:
Would a (single target) spell similar to Harry's Gravitus (in Changes and It's My Birthday, Too) also be resisted with Might, instead of Athletics?
Also, how would a Zone-Wide attack be defended against, narratively? I mean, if for example Harry did a Zone-Wide Fuego, how could someone justify avoiding being hit by it, other than someone who would be able to dive out of the zone?
Gravitus has always given me heartache trying to simulate in game, because of the side-effect... one of my players wants to try an earth-mage with strong evocation, and I'm not sure how best to simulate it. IMO, it should be two simultaneous effects- one massive damage effect, fairly localized (single target or single zone), with surrounding zones taking a low-level maneuver to lose their footing. I could just call that fluff- but it's certainly big and noticeable if, say, someone tried it in a city.
On the upside, every time we've seen Gravitus, it's been closer in line with something thaumaturgy could do than evocation, systems-wise... it certainly seems to be more of a prep-work kind of spell with harry- having to gather power, focus his mind... affecting an area so large that not all of it can be within line of sight... that would solve it easy.
A lower-level version, I'd run as a direct attack, using evocation, and call it done.
Changes-grade... either involves a TON of FP and tags, or thaumaturgy.
And I'd make it resisted by Endurance (modified by Might) either way.
As for defending against zone attacks- easy... Cover. Dropping prone might even be enough, depending on the spell's visual description.