RNS315 Microphone volume

Hi, I've tweaked the microphone in my RNS315 up to 25dba but people still say they can hardly hear me unless I talk really loud with windows up. I'm using the microphone in the overhead connected to the RNS315 back. is there a better mic or any solution for my volume?

Thanks

unless you talk seriously quiet it should not be a problem.
is the RNS315 a factory installed radio in your car? or did you swap it in?
(reversing the mic wires will cause low audio levels and poor audio quality)

I messed with the mic's dba setting at one time, something in my failing memory suggests that the higher the value the lower my voice volume seemed.... but again my memory sucks, I could be thinking about something else, or even another car entirely. (getting old sucks)