homekit devices work across different networks?

I bought and installed an iDevices switch for my external garage. I have a wifi network for my house and then an extender, with a different SSID, that covers the detached garage. I setup HomeKit by pairing my phone with the garage SSID and it works great , when I'm on that network. If I'm on my home wifi network it says the device is not responding in the Home app. Switch to the Garage network and it finds the device just fine. I also have an Ecobee thermostat paired with my home network, but it works and shows up fine even on either network. Note the iDevices app has no issues either whether I am on one network or the other. Is there some limitation specific to HomeKit and all devices must be on the same network, or is it specific to the iDevices switch? Hope my explanation was clear. Thanks!