Signal strength of Esp8266

The PA written on the esp8266 is +25 dbm . I have an app in phone that can read the RSSI from wifi connected to esp8266 .
When the phone ( app ) was brougth near the wifi module , it reads as -20 dbm . This is not true because the app should show +25 dbm .
Can u explain the error that has risen . I had done this observation in open ground where there was no building around .

The app that i used was Airport Utility in iphone .

Hello @alenvarghese10 I don’t know much about the topic but I have tried getting some information. I have some images please see these images.