If your SDR is -125 to -130 dbm everywhere, the noise blanker is probably the last thing you should be worried about. I'd try another antenna, maybe about 30' of hook up wire running out a window.
Something is not quite right here..perhaps our reference values we are looking at.
All the You Tube videos I look at concerning the G31 are all showing about the same noise floor. (-125 to -135) which is obviously extremely low. My guess is that these are relative values on the G31, not absolute calibrated values.
Recently I put up the Par Endfed EF-SWL....Hugh difference in quieting the noise with fantasic ability to receive wek sigs...but still, the "Noise Floor) visually indicated on the G31 is averaging -130dbm.
As reference only, Radio Havana signal on 6 Mhz is peaking around -60 to -70. Monster signal obviously.
Hopefully we are all on the same page as s/n are concerned as 0/dbm would represent s/n= 100/0