More bugs
Bless from my ally made me lose concentration on hex. A missed attack from an enemy made me lose concentration on hex.
More opinions
I don't think making characters burn works well with concentration since every time a 1 damage tick on a burn effect can disrupt concentration. This heavily nerfs concentration spells and firebolt is kind of broken because of this. I also think the surface mechanics in general is to much, it was fun in DOS 2, but does not fit here.
