Let's start with enabling the EFR32 high-power PA for maximum output power (19.5dBm) in Hardware Configurator.
- In PA block, set PA voltage to 3300 mV (as opposed to 1800).
- In PA block, make sure "Use low power PA" is set to False.
We also have an application note that covers setting up the power curve for your design:
"AN1127: Power Amplifier Power Conversion Functions in RAIL 2.x"