Looks like the default was 49.6 dB. I just picked a gain number out of the air and set it to 40.2 dB.
pi@piaware:~ $ cat /etc/default/dump978-fa | grep gain
RECEIVER_OPTIONS="--sdr driver=rtlsdr,serial=00000978 --sdr-gain 40.2 --format CS8"
I’m not sure how to set a UAT978 receiver to the optimized gain… But I did see a few planes out 10nm!