When I was doing Zacharius' cementary on Saturday, these deadly Champion archers definitely focused low AC characters too (and their placement was a bitch...).
Or these encounters with mostly ranged Drow parties (low Fort on them though ).
I think there are some enemies who always scripted to choose lowest AC in both games on any difficulty (like those maniacs from Pitaxian Palace & Linzi situation or Good-Smiting gargoyles from Wrath), but still, I had got through ch 1&2 with barely one point of damage on Ember & Nenio on Core, but on Hard they were constantly pin-cushioned by the Ghoul Hunters from the Chapel.