Haven discussion.

The "Cry of Horror" is simply an improved version of the "Banshee's Cry," so it's -6. It's unknown (at least, I haven't checked) how it works for the Daedra... but the maximum is -7. Astral creatures don't count... because it's an active ability. But theoretically, anything is possible, meaning it could be another -4. = -11
Plus, rings could add another -4. Zombies are -2/-3, I don't remember.
How to get -22? Only if playing as Necromancers, and only with other units.
If you also use undead-boosting artifacts, you might be able to try for even more, but morale might still outweigh it in that case.