How to change AD9371 transmission gain?

We use ADRV9371-W and ZC706 with No-OS Setup.

We want to set as high transmit gain as possible without an external PA.

Although 1 [MHz] and 0 [dBFS] CW were prepared and transmitted as transmission data, only an output of 0 [dBm] was obtained.

(This value takes into consideration the attenuation from the ADRV9371 TX1 terminal to the measuring instrument.)

However, according to the answer of following URL, 0 dBFS corresponds to 7 dBm for a CW tone and for any other digital input output power will be relative to 0 dBFS.

Where does this difference in output power occur?

And how can it be changed?