No tech here, just a player, and I also have that feeling that AI NPCs go for the weakest one first among a group of opponents, only if it's not too far. But most of the time the closest one.
I never saw a monster running for the wizard at the end of the map. I'm always front row anyway, even with casters, but I run fast. They will go for me first, being the one theu followed, the one who "triggered" them, if I rejoign with my companions, but switch to one of them, 2 seconds after, if I keep fleeing.
And die.