Tp link Mr3420 v5 Txpower

Hello i currently use mr3420 v5
and using openwrt latest snapshot Tue Oct 6 19:54:25 2020
tx power is only 18 dbm meanwhile on official firmware is 20 dbm and on real world use it varies between 1-2 bar, link speed also changes, already tried official build still 18 dbm.
already region to BO/TW, change via iw txpower doesnt work
and jow reghack is only for atheros devices, on mr3420 v5 based on mediatek can i use it?
thanks for any feedback