There are two separate settings for 2,4 and 5GHz bands. As I know according to standards in Europe the 5GHz indoor Wi-Fi has 23dBm (200mW) EIRP limitation.
So If you want your 2,4 and 5G cells have the same area you need to configure the 5G attenuation 3dB less as 2,4GHz. becouse of higher FSPL in 5GHz (approximately 7dB)
For your example it will be:
13dBm EIRP (for 2,4GHz) + 7dB (FSPL difference) = 19 dBm EIRP for 5 GHz
23dBm (max EIRP) - 19dBm = 4dB attenuation for 5GHz