HKIRD are rightly saying that if you work for CX you are automatically HK based
Not quite true. HK tax is based on the
source of the income, irrespective of domicile, residency, etc. Although basees are paid in a foreign country, HKIRD has rightly determined that the income is sourced from HK, and is therefore taxable in HK.
That said, the taxable income is reduced according to the number of days spent in the foreign jurisdiction (eg. Australia), provided tax has been paid in that jurisdiction.