I'm doing some last in-depth testing to optimize all the device settings for the best energy resolution possible and it looks like I found a much better suited setting for the ADC "averaging". In my case, I was able to get an improvement of about 1% just by switching this setting ("set averaging 2" from the default value 5). I've also just now changed the default value for averaging to 2 in the 4.x.x firmware to apply this improvement. If you already changed something in the settings, or you're using one of the older board revisions, you'll have to edit it manually.
Give it a try, it might even work on older board revisions, but your mileage may vary. Nothing can break, so just feel free to experiment. If you're not sure, just reset the settings afterwards and you're fine.