Jurgen, I dont know the specifics of Synology upstart I am afraid. I think a more maintainable solution may be to host the Weather Service on your OSPi. This would take one machines out of the equation and you could then use the systemd method to keep the service running. Just a thought. Not that every time the Weather Service restarts then it takes around 24 hours for the scale to stabilize as it ideally wants to use a full 24 hours of information.
The location is not used by the Weather Service when in PWS mode to calculate watering scale. The location is however used by the App to provide the “current” weather conditions and the five-day outlook that you get when you click on the weather icon. These are two different things.