Heroku is only available in EU and US east. Latency from Australia is somewhat unavoidable. You can maybe reduce it by using Cloudflare or similar to terminate TLS as close to your users as possible.
Cloudflare give different Anycast IPs for each plan and they don't always hit the local ingestion point. Some people shot themselves in the foot with free/pro plan in certain markets (India, aus etc..) I don't believe in May 2021 local ingestion (TLS termination) is happening on anything less than Business plan in MEL or SYD
