In your case take a look under Country selection, try to set it on No_Country_set) and take a look on Current Tx power tab.
But i have another weird problem. Recently bought R52Hn (Manual says "Output Power of up to 25dBm @ a/g/n Band") but mine runs Max 22dBm under 6Mbps. Country mode No_country_set, Tx power default, frequency 5180.