mate most tax accountants here know the tax rules.....Aust. has a DTA With Thailand so you will be taxed there. Now where does your Hong Kong Dollars go? Thailand or Australia? What Visa do you have here? Who long in a continuous period to you stay here.? Does Hong Kong have a DTA with Thailand? So I know what you asked but there are lots of questions. Now I received advice with an Aussie accountant and Thai one here in Bangkok and both gave me the same advice. Also your residency is in Australia but that wasn't clear to me
My tax liability is in Australia.
So use Google maps find a couple of Tax accountants in Phuket and give them a call. Its really that simple. Oh why didn't you post on a phuket fb page too?
Why not ask the airline your flying with? If they require an onward travel ticket within 60 days simply buy an onward travel ticket at 60-days and your normal ticket at 90 days