TX Power from ru_metrics does not change with tx_gain

[jaiglesias-optare]

I am using USRP B210 to perform DL bitrate measurements with iperf and a Quectel RM530N-GL modem as UE.
I would expect that changing "tx_gain" would cause Tx power to change accordingly. However, what I see (using "ru_metrics" command from gnb) is that average tx power remains approximately constant in range (-13, -15) dB when changing tx_gain from -64 dB to 89,75dB.

Is this the expected behaviour? What am I missunderstanding, then?.
Thank you very much!