https://www.thethingsnetwork.org/forum/t/determine-which-gateway-is-used-by-a-given-node/11531 should get you going? For example, it explains how to search by location.
Peeking in https://www.thethingsnetwork.org/gateway-data/ I assume all those Sydney Water gateways are owned by @maj, so you can be sure their configuration is very much okay. Hence, if there is no overlap in uplink channels for the frequency plans (which I did not validate), then I’d assume that the gateway would support the expected downlink channel when it has forwarded the uplink. (Just very much assumptions though.)
You may want to move closer to the gateway for testing?
Aside: subscribing to the MQTT events and persisting those will really help debugging.