Does Atziri's loot in temple scale with monster % rarity or scaled as a Chest-loot?

I'm trying to comeup with a spymaster chain for lock sustain and build up a monster rarity or chest rarity for Atziri loot. The thing is i couldn't find any existing discussion about what actually scales her loot. You KILL her and then open CHESTS. So there's two conflicting mechanics there.

Unid Atziri's Splendour is 145d as of writing this post btw.