clarify that zones are based on the bottom center

docs/docs/configuration/index.md

@@ -386,7 +386,7 @@ cameras:
       #       camera.
       front_steps:
         # Required: List of x,y coordinates to define the polygon of the zone.
-        # NOTE: Coordinates can be generated at https://www.image-map.net/
+        # NOTE: Presence in a zone is evaluated only based on the bottom center of the objects bounding box.
         coordinates: 545,1077,747,939,788,805
         # Optional: List of objects that can trigger this zone (default: all tracked objects)
         objects:

docs/docs/configuration/zones.md

@@ -3,7 +3,9 @@ id: zones
 title: Zones
 ---
 
-Zones allow you to define a specific area of the frame and apply additional filters for object types so you can determine whether or not an object is within a particular area. Zones cannot have the same name as a camera. If desired, a single zone can include multiple cameras if you have multiple cameras covering the same area by configuring zones with the same name for each camera.
+Zones allow you to define a specific area of the frame and apply additional filters for object types so you can determine whether or not an object is within a particular area. Presence in a zone is evaluated based on the bottom center of the bounding box for the object. It does not matter how much of the bounding box overlaps with the zone.
+
+Zones cannot have the same name as a camera. If desired, a single zone can include multiple cameras if you have multiple cameras covering the same area by configuring zones with the same name for each camera.
 
 During testing, enable the Zones option for the debug feed so you can adjust as needed. The zone line will increase in thickness when any object enters the zone.