FF6 Curse of the Gods - full game hack project

Yeah, Atma Weapon shouldn't be affected much at all. As has been said, its damage modification based on the wielder's missing HP related to their max.

The Valiant Knife, on the other hand, has a flat +1 damage for every point of HP its wielder is missing. So if you manage to keep that character's max HP in the 9000s and run around with them in near death state, they'll be getting greater than 6000 bonus damage just based on their missing HP.