Under what circumstances would one increase the AF out on the Receiver for wireless lapel mics?
Currently we just increase the Gain controls on the H6
Before modifying the receiver output level from it's nominal level, check that your gain settings on the transmitter are properly set (the audio is modulating in the appropriate range on the radio link).
Then set the recording level of your recorder to have proper levels on the recorder.
Depending on the recorder and it's input sensitivity, you might find that this requires either to have a very low input gain (in which case it might be interesting to lower a bit the receiver output level) or to have a very high input gain (in which case it might be interesting to raise a bit the receiver output level).
Approximate clues for a high/low input gain on the recorder inputs : if you are in the higher/lower 20% of the input gain control.