AP’s have their tx power shown per antenna chain based on channel/compliance table power settings rather than per radio
The formula is to add for:
1 chain = +0dBm
2 chains = +3dBm
3 chains = +5dBm
4 chains = +6dBm
The GUI does not take any antenna gain into account.
As an example: 10dBm in the GUI, assuming 4 radio chains = 16dBm. If the AP510 only has AF power, you would see 13dBm as 2 radio chains are dropped in lower power mode.