You got it wrong.
If it was Piaware 3.5 SD Card image, it will be “pi@piaware” , not "pi@raspberrypi"
Your install is Raspbian Jessie image with Piaware and dump1090-fa add-on
In this case sudo piaware-config command will be saved in piaware.conf file, but will NOT be transferred to dump1090-fa settings.
You have to edit file “dump1090-fa” and change gain setting.
(1) Give following command to open file dump1090-fa in editor nano
pi@raspberrypi:~ $ sudo nano/etc/default/dump1090-fa
(2) In the file opened in nano, change gain -10 to 40 (Caution: do NOT use negative value **-**40).
RECEIVER_OPTIONS="–device-index 0 --gain 40 --ppm 0 --net-bo-port 30005"
(3) Save file and close editor
(4) Now restart dump1090-fa:
sudo systemctl restart dump1090-fa
(5) Check status:
sudo systemctl status dump1090-fa -l
Last line of output will show gain actually set:
raspberrypi dump1090-fa: rtlsdr: tuner gain set to 40.2 dB