You can go much smaller than 400ft with Geolocation. A good system also allows multiple geofence methods not just a circle. It depends on the device being used. Even with some cell phones you can go very small...
https://forums.simplextech.net/threads/how-to-use-in-homeseer.11/post-16
One user in testing setup a 10ft geofence inside their home. It worked. YMMV as always.
