Environment : IAP-175; Version: 220.127.116.11-18.104.22.168
By default Radio 0 on IAP-175 is used to serve clients as well as used for back haul connection to mesh point/portal. With default configuration, RSSI LEDs against Radio 0 display the RSSI it hears form the other node (Mesh point or portal). So when you are not using any mesh links with IAP-175, the RSSI LEDs against Radio 0 will not glow.
Enabling "Extend SSID" option under Advanced Settings disables the Mesh Links and LEDs against Radio 0 will start to glow even when it is used for coverage only.