why RSSI goes smaller when inject out-of-band tune?

Hi,

the working scenario below:

Device : AD9363

ADC work mode: MGC

work frequency:1440MHz

Bandwidth: 8MHz

when we test noise floor without injecting tune, the valud about -93 dBm

when we inject tune @ 1430MHz (out-0f-band , signal strength about -40dBm), we got the noise floow -125 dBm  meanwhile the VGA = 0x4c (the max value)

Can you help me explain how this happed?   thanks very much~~~