Hard to tell anything without knowing how you are measuring the signal strength.
Measure the signal strength using a laptop and a WiFi scanning tool like Netspot, Acrylic WiFi, inSSIDer, etc. If you don't have a laptop you can use an Android device and the WiFi Analyzer app. These tools will show you the signal strength for all Orbi devices simultaneously. There will be two signals per Orbi unit. This will let you see what's happening.
