Thoughts on optimizing gain

The change between max and 42.1 is actually quite large. It’s possible however, that if your antenna is blocked by obstacles or terrain, you are already receiving everything inside that range, so increasing the gain isn’t increasing the signals significantly - any increase from getting marginal signals could be easily offset by losses from oversaturating the strong signals.

I take it from your previous post that you are using the mag-mount antenna cut down to the correct length? If so, then you can likely increase your receiver performance a lot by swapping it for a simple home made antenna (or one of the pre-made options you can get).

See one of abcd567’s many threads on building and optimising antennas - the spider based on a chassis socket is a good place to start: