FIR filter affect the RSSI reading

Hi,

We are using the AD9361 on a custom board with the no-OS driver.

1. We noticed that when we replace the FIR filter, the RSSI reading changes by approximately 6 dB. Could you please explain why this happens?

2. What is the purpose of "rx_gain" in the FIR filter structure in the RX path? is it Digital gain?

Thanks

before:

AD9361_RXFIRConfig rx_fir_config = {
3, // rx
-12, // rx_gain
1, // rx_dec
{-9,35,30,116,144,218,208,165,6,-204,-462,-651,-702,-508,-66,578,1247,1722,1750,1173,-24,-1629,-3229,-4262,-4162,-2510,811,5540,11039,16412,20690,23062,23062,20690,16412,11039,5540,811,-2510,-4162,-4262,-3229,-1629,-24,1173,1750,1722,1247,578,-66,-508,-702,-651,-462,-204,6,165,208,218,144,116,30,35,-9,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}, // rx_coef[128]
64, // rx_coef_size
{1024000000,256000000,128000000,64000000,32000000,32000000}, // rx_path_clks[6]
8068964 // rx_bandwidth
};

after:

AD9361_RXFIRConfig rx_fir_config = {
3, // rx
-12, // rx_gain
1, // rx_dec
{-5,17,14,57,71,110,107,88,10,-95,-227,-326,-359,-270,-54,268,612,866,902,635,49,-758,-1586,-2153,-2173,-1424,167,2487,5230,7954,10171,11465,11585,10509,8452,5806,3054,649,-1079,-1982,-2102,-1639,-868,-72,539,848,855,635,309,-12,-238,-343,-325,-236,-109,-4,77,101,108,73,59,16,18,-4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}, // rx_coef[128]
64, // rx_coef_size
{1024000000,256000000,128000000,64000000,32000000,32000000}, // rx_path_clks[6]
8068964 // rx_bandwidth
};