PA gain with bias setting and die technology

Hello sir,

I'm just a beginner who is much interested in transistor technology.

I am using a cellular PA with high/low two gain modes.
When I asked the supplier how the different gain is implemented, the answer is that it's due to different bias voltage.

But from my understanding, bias setting impacts the transistor efficiency, not gain,
gain is more related to transistor β value or external feedback resistors.

Am I wrong?
Look forward to your kind explanation.

Thanks in advance.