Hi KW - Thanks for the input. Unfortunately, because the effect I want to apply is spell absorption, an entry point won't work as there don't seem to be any that allow you to change an AV.
I've rewritten this reply 3 times now! Each time I had another idea, looked stuff up, started writing and then thought of something else. Rinse repeat!
Anyway, now I think that my idea would never really work, as the absorption effect runs on the player, not the incoming spell, so even if there was some way to trigger it only if the player was being attacked by elemental magic, the player would still have a chance of absorbing any other magic from other casters for as long as the ability was active. I think I just have to be content with adding a small boost to spell absorption and maybe a small boost to elemental resistances as well.