High Ground Gives Defense (WotC)
Gives units lower than the target they’re shooting at a -10 aim penalty.
I haven’t tried it myself, but it sounds like it’s not compatible with EU Aim Roll.

XCOM 2 Mods Catalogue
Gives units lower than the target they’re shooting at a -10 aim penalty.
I haven’t tried it myself, but it sounds like it’s not compatible with EU Aim Roll.
