I was thinking that for Fireball ballistic armour would probably be effective, but maybe not the Met vest (and we know Natural Toughness doesn't work). In coding terms I can add toggles to each spell to say what armour works against a spell (e.g. Ice Blast has all options tuned off, maybe Fireball has Ballistic turned on etc). But if the official line is a bit more of a blanket approach then I'd code that in.