I'm almost sure that there are mobs that "sense you" from different distances, but this was almost impossible to be proved regularly because we were supposed to see the mobs "interacting"/moving regularly or not moving at all. Either way I can relate from my experience with a friend in OTS.
When he was using a gamemaster character they didn't move at all (mobs didn't sense him at all) until I approached 20 or less sqm from these mobs so they started to "sense me" and "to interact as alive mobs" (hydras in that case)
Yet as I said we aren't supposed to see those mobs in that "idle status"* and that could be considered as a glitch, and sadly my information can't be supported and it is possibly outdated.
but facts are:
- yes, certainly there is a distance in the same floor which once reached the mob doesn't sense u anymore and doesn't interact/move until someone approach
- to test this regularly is needed an undetectable observer (probably a 2 floors higher place or 2 floors lower) and a large place (20+ sqm 30-40 if possible)
- we aren't supposed to see this.
a good place to test this probably could be the mushroom pigs ground (in the gnome base where u do "digging" task) because have a +2 place and a "large" place
After visiting some places i found that under Fenrock (on the way to dragon lords) there are a lot of bridges which allow you to notice this "glitch", u can easily go +3 from creatures and they will not move, also i found that they can as well stop moving if u see from a lower position than their floor.
if someone want to test it and have the specific place probably would like to know:
- maybe the mob sense npc (merchants, etc)
- maybe the mob sense another mob enemy
- the mob must be far from any thing that he sense as "playable character" or probably "enemy alive" to actually stop moving
Update: adding info to the research as well fixing some misleading