There is a village in the South [3237.08,7794.73,0.00161934] where there is an empty field. And AI can walk and pass this field. But if they are there, they can't see others and other AI can't see them.

Test: put three VC and three US soldiers there and give them a search and destroy waypoint. They will run up and down, but will not fight until they are closer than 3 meter. The field is open. Me as a player can see them and can kill them. But they not see me and not shoot me.