[Avenstar]

This is only an observation, but I think that when you are higher level than the level cap of the zone, only the lower level monsters will spawn. This could be to prevent having to fight multiple low level battles not worth the effort when you are travelling around.

For instance, while traveling on Arnika Road at level 21, the only monsters I came across were a group of 1 sige/5 bandits, all level 6.