HomeKit Homekit Geofencing parameters

I think this article should address your question:
https://www.askdavetaylor.com/how-automate-devices-apple-home-homekit/

Basically, you can set and see how far you'd have to be away for the geofence trigger to activate by dragging the circle.

 

--- Post Merged, Feb 6, 2018 ---

What is happening with me is that when I attempt to set up a geofence automation, the default location is "Home", but I cannot define a radios from the "Home" location like I am able to do with any other location. If I put in my full address for the location, I can define a radius. However, I do not want an automation entitled "When I leave ... my address" instead of "When I leave Home." I this a bug or am I missing something? I

 

I’m wondering the same thing!