Chase - 50m
Attack - 10m
Guard Me
Prioritize melee
Follower set to Guard Me behavior won’t engage an enemy archer shooting me with arrows if the arrows are blocked by shield and will only engage if I let arrow hit me for damage.
This issue is still present in the 11.04.2020 patch.
Follower set to Guard Me won’t engage in combat so long as I defend with a shield, but will engage after I lower shield and take damage.
Which suggests that the thrall’s agro is initiated by ‘Player took damage’ instead of ‘Player is the target of agro’, eh?
Computing the first would only involve the player; determining the second would require continuously monitoring all NPCs in the area and lead to the thrall trying to attack something that is inaccessible.