Use feeder id of 1090 Pi (SITE 35253) on 978 Pi (SITE 182246) also, i.e. both Pis to have same feeder id.
EDIT: Option-2 (UNTESTED) T E S T E D
In 978 Pi
sudo systemctl stop piaware
sudo systemctl mask piaware
sudo systemctl stop dump1090-fa
sudo systemctl mask dump1090-fa
sudo systemctl enable dump978-fa
sudo systemctl start dump978-fa
## REBOOT
sudo reboot
In 1090 Pi
Note: in the 3rd command below, in place of 192.168.xx.xx, use your 978 Pi’s actual local IP
sudo piaware-config uat-receiver-type other
sudo piaware-config uat-receiver-host 192.168.xx.xx
sudo piaware-config uat-receiver-port 30978
sudo systemctl restart piaware