Multi router 'floor' detection with OpenWRT - how to

Searched for this but surprisingly found nothing.

Two OpenWRT devices here. One as router downstairs, the other as access point upstairs.

The router is already running, the access point will follow.

The thing is, to have advanced automation Home Assistant (Hassio) should know whether a device is upstairs or downstairs.

I tried a custom source_type in the openwrt_hass_devicetracker script but HA refuses this.

2018-12-16 18:05:21 ERROR (MainThread) [homeassistant.core] Invalid service data for device_tracker.see: value is not allowed for dictionary value @ data[‘source_type’]. Got ‘router_sb1’

How to pass location data with device_tracker ánd how to use it in automations?

Same question as in topic:

It is possible to have the script set location_name, which overrides the home and not_home states. Would this be a good idea or will it break lots of things?

Kick before splitting question into new topic.