I'm not talking about creatures, but about blocking reset floor - and yes, we can do it by standing on a lower level, as well as on the higher level. Monsters from the nearest levels can "see" you. That's why they're moving. If monsters don't see any character then they are static and don't move. You can observe it on deeplings or Fermor Hills. What is more by standing 30 minutes you can prove nothing, because you probably didn't block any reset floor in such a short time - we're talking about camping it few hours.