Apple Watch as primary location device

So, I have a front door lock that works with HomeKit to unlock my door once I come within the defined geofenced area around my home, and locks it once I leave the geofence boundary. It works just fine.

However, I don't always have my phone on me: when I go run, I leave my iPhone at home and run with just the (cellular) watch. Because of how Location services seems to work by default, even though the Watch does know when it is out of range of the phone and will share it's own location with Find My, because my iPhone is still at home, and is considered the primary location device, the door locking and unlocking with the geofence doesn't work when I go for a run with just the watch.

ISTR there being a way to set the Watch as the primary device for location services, but I can't seem to find it now. Does anyone have any ideas? I called Apple Support, and the best they could come up with was to turn the phone off when I go for run. That would probably work, but it seems silly because this should be a simple software configuration thing.