ZWave connection between device and controller/extender

A few days ago I have installed a Range Extender 7 (Aeotec) in my environment with ZWave ZStick Gen5 (Aeotec). The reason was to get a connection to following device: door sensor, 15 meters from Extender, only back wall of a garage between. The connection fails. I was surprised, because my other 35 zwave devices which are distributed over a 3 floor building with concrete walls are working quite well.
My question is: how can I recognize whether the door sensor is connected to the Extender or to the Main Controller (ZStick)? I would take the door sensor close to the extender.

The only way to truly know is with a zwave radio sniffer (zniffer). I have found with zniffing that z-wave routes can be tricky and what seems logical might not be.

Was failing before and now works or is failing both before and after the extender. Did you try to heal the sensor (will need to wake it). If you have the binding in debug and run the file through the zwave viewer, you might get an idea based on the time stamps.