Ranked ping in Perth, Western Australia is constantly 150ms +

I consistently connect to ap-southeast-2 since that server is in Sydney and it is the closest server to my location. When I play wildcard game modes, I get the expected ping of around 60ms, which is a playable amount.

As soon as I enter a ranked match, I suspect I'm being matched into ap-southeast-1 servers, because I consistently get ping of above 150ms, which is not really that playable. Regardless of whether or not I'm being moved to a different server, this ping degrades the experience playing on ranked and I don't know of any solutions I can try on my end. This is because I know the ping isn't caused by an issue on my network due to servers on the Wildcard game mode working just fine. 

Thanks in advance for your help