Detection confusion

I’ve had my camera for a while now, and it works pretty well. But I remain confused about the relationship between “detection zone”, and “PIR effective area.“

It seems like I only get notifications when there is movement within the PIR area. So what exactly is the point of setting a detection zone at all? Why do I NOT get notifications or recordings for movement within my detection zone, if that movement is outside my PIR area?

Maybe you can find your answer here;