¶ Radius
Radius on Triggers and the 
Area Condition are calculated as real 3D spheres (not blocky spheres) with their center at the chosen 
Position. The figure below shows a top-down view of how the radius works.
If the radius of a trigger is set to 0, then the trigger is simply disabled. If you try to decrease the radius below 0, the radius will be set as INFINITE, meaning that the trigger will work no matter the position of prey.