After power cycling the bridge the sensor to bridge RSSI improved from -70 to -58. Thanks for letting me know that even -90 is ok.
The reason I suspected something was wrong with a -70 RSSI in my case it that I activated the sensor inside the house where the RSSI was in the -50 range. Then I moved it just a couple of feet outside the wood and glass front door where it dropped to -70. Given the nature of the Smart Lighting radio signal, such a large drop through a door didn’t make sense. Fortunately it was easily resolved.