Setting several registers may change the behavior of the device (reading distance, quality of communication with tag, etc.) These registers affect the parameters of the receiver and the transmitter.
RFCfgReg configures receiver gain and RF level detector sensitivity. Increasing the gain of the receiver can increase the operation distance, but the influence of the environment increases. As a result, the number of errors in communication with the tag can be increased (especially at a certain problematic distance).
Please, download the detailed RF analog register setup guide.