This is a nice change. A bit more realistic. However, I think it needs to be tweaked a bit.
I tend to solo, because I never know when I will be on, (sometimes with a hireling and/or summoned monster) and have found some scenarios a bit much. Do a ranged attack on one and suddenly there are thirty headed your way? Not good for a rogue or non-melee.
I don't know how you have it programmed but could you back it off a hair or two? Or maybe have three levels: one for solo, one for small groups and one for larger groups?
Just my 2 coppers.