Hi Peter
It's impossible to generalise and I'm not at all familiar with ACT strata law but I know in NSW and elsewhere, if you doubled the size of your home, even if there were exactly the same number of people living there, your neighbours would expect you to pay roughly double the levies.
Unit Entitlements are challenged fairly often here, especially when developers have set up a strata promising low levies to the purchasers of their premium properties.
We had a case here where the owner of the penthouse in an inner city block was paying less than the owner of a one-bedroom flat on a much lower floor … until they were taken to the CTTT.
That said, challenging UEs can be very complicated and stressful so it's not anything anyone would take on lightly.