--gain and -10 are the entries that piaware added in their latest update (1.20). I didn't see much difference, but I have a crappy antenna setup which limits my receiving distance anyway...
From the piaware release notes:
piaware 1.20-1
- Greatly improved range and message rate by configuring dump1090 to use auto-gain rather than max gain (--gain -10 added to dump1090 arguments). Sites allowing remote upgrade will be upgraded automatically. People running their own copies of dump1090 are advised to add --gain -10 to their dump1090 command line arugments to obtain these same improvements.
pi@piaware /etc/init.d $ more fadump1090.sh
#!/bin/bash
### BEGIN INIT INFO
#
# Provides: dump1090
# Required-Start: $remote_fs
# Required-Stop: $remote_fs
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: dump1090 initscript
#
### END INIT INFO
# Fill in name of program here.
PROG_ARGS="--quiet --net --gain -10"
. /lib/lsb/init-functions
DAEMON=/usr/bin/dump1090
PIDFILE=/var/run/dump1090.pid
test -x $DAEMON || exit 5
LOCKFILE=/var/lock/dump1090