As the presence sensors (and geofencing) are not always accurate, the most efficient way to set your ecobee thermostats to Home or Away is also to use multiple motion sensors in your home to detect if there is really somebody at home or not.
You can then leverage all your ST connected presence/motion/temps/contact sensors by using my smartapps built around My ecobee device which is the most comprehensive ecobee-ST integration.
The zoning smartapp called ecobeeSetZoneWithSchedule leverages all the ecobee climates settings (or scheduled programs) set at the ecobee portal and can adjust your thermostat setpoints for your far away colder/hotter rooms or set your thermostat to Home or Away using your existing ST connected temp/motion/contact/presence sensors. For each room, you can also customize the occupied threshold for better presence detection.
On top of it, My ecobee device can even give you some comfort and energy savings tips based on your actual indoor/outdoor conditions at your home (ex. runtime stats for each of your furnace/HVAC components)
If you have the Ask Alexa smartapp, it can give you the tips verbally through your Amazon Echo speakers.
Refer to this thread and the ST community wiki for more info:
http://thingsthataresmart.wiki/index.php?title=My_Ecobee_Device
Regards.