QF does have a policy that separate domestic tickets which connect to an international ticket will get the QF international allowance ... not sure of the restrictions (probably it has to be a same-day departure for domestic/international arrival). They introduced this policy a few years ago to encourage international tourists to book on QF instead of the competition, so presumably it is somewhat leniently enforced. As for your question on whether the self-check kiosks measure the external dimensions, I'd say not but don't have any inside info about how they work. Looks to me that only weight matters as for example they allow using a large tub to hold irregularly shaped bags (and that would exceed the size limits if counted as baggage size).