It was hard to find the right setting because it wasn't possible to listen to the recording while in the aircraft due to the noise
Going back to what we use to do -
(a) always set up in the aircraft with things running using an earphone from the camera
(b) interestingly (and I have no idea why, being a greaser rather than queer trades fellow) for a given installation there was one pot setting which worked noticeably well
(c) you may have to try several resistance values to get a satisfactory result.
(d) I doubt that I have any archive audio but it certainly worked fine