For the last 15 minutes that is 36727/(228785+20291) = 14.7 % of strong messages. (>-3dB, nearly too strong to be received hinting that you didn’t receive some stronger messages because the signal was too strong)
You should probably try 49.6 instead of -10 now for the gain 
Probably higher message rate but not sure if it would cut range, probably not much if at all but hard to say without testing.
Oh and the red area in the Message Rate graph is kinda bogus, it represent the derivative of the messages > -3dB which is not that useful.
I’ve written a fix you can read about and download if you want:
(Optimize Gain - which would you chose - #174 by wiedehopf)