The following explanation should help you understand why the HF ATT value does not change： RxP and RxN need to be connected to the antenna circuitry via a serial capacitor (for the DC decoupling) and a serial resistor (for the voltage level reduction). In combination with that external resistor, the HF attenuator block controls the RX input voltage level in such way that the RX always gets a proper input signal. This control loop is done automatically, and there is no direct user setting required. Reading the HF_ATT_VAL (RXCTRL_STATUS register) retrieves a 6-bit value, which corresponds to the RX carrier input level, and therefore can be used to optimize some settings and adjustments.
