what??? i think that is impossible lol, unless its a doodad, but terrain??? maybe your spawning too many units in a spot, OR the unit could be spawning at the point on the outer edge of the region, and when that happens, the unit acts like it never enters the region. what you should do is make a smaller region inside the bigger one, then spawn the unit inside the smaller region, then make the triggers in the bigger region, that way the unit always triggers the trigger.