The wiki says that monsters target the first player they see or the player who has done the most damage to them (modified by threat).
This clearly isnt true. When I did the grotto after TRing, i hid at the end of the corridor after opening the door to the priestess room. One of the sahaugin pushed its way past the NPC adventurers (who were blocking the doorway) to run at me even though i was hiding in the rear and doing absolutely nothing. I obviously had zero threat at this time and the NPC adventurers who were doing damage should have a threat higher than zero.
It is also extremely common to see enemies ignore the front liners to run at the people in the back who are doing nothing. Park a healer hireling far behind you and enemies will ignore you to run at him, even if you are doing damage to them and he is just staring at the wall.
When I did chains of flame yesterday, I kept seeing enemies ignore the front liners to go after the healer hirelings who were parked in another room...even though there were multiple doors/walls in the way and the enemies couldnt possibly have seen them.
This makes me wonder if enemies are bugged and ignoring LOS/distance considerations..hirelings parked in another room will constantly try to attack enemies through walls/floors so im wondering if maybe NPCs are bugged in general and ignore LOS/distance factors? Even if you leave a hireling at the dungeon entrance, they will constantly try to attack enemies everytime someone else in the party aggros an enemy. Even if it means standing in place and hitting the air with a quarterstaff.