Different subnet cannot resolve IP via Pihole

OS: Synology
Upstream router: eth1:, eth2:
IP of Synology:
IP of Pihole: (setup as "Use the same network as Docker Host")

IP within is able to resolve IP via Pihole but not another subnet I can see the DNS traffic from on Synology with tcpdump but there is no return traffic from Pihole.

Does anyone know additional network setting is required for another subnet?

Check out your DNS settings on the Pi-hole dashboard. Is this box ticked?

Screenshot from 2020-12-25 20-50-25

If so, there you have the answer why queries from eth2 aren't replied to. This is typically a good choice, however, in your particular case not. Chose one of the other two settings and it should work.