New corrupted (greater) essences MIA, just bad luck?

Even after fully investing atlas points into the Essence branch for increased spawning/chance at greaters & double-corruption, I have yet to see any of the new Essences of Insanity/Hysteria/Delerium/Horror.

Sample size of one, I know. Has anyone else been able to spot 'em?

If so, how do they modify the encounter?

Nope. I also had only 4 regular greater essences in 200 hours so far. Either might as well not exist in the game.

Tough to tell... When it first dropped I corrupted every essence monster before remembering that I needed the vaals for t16. Didn't get 1... I vaaled maybe 30 before stopping. Ssf