Camperdown airlines particularly legacy carriers rarely offer genuine discounted tickets Directly to the public in large numbers. No what they do is package up their over supply - usually in the back of the bus and dump it to the market place via the consolidators.
Btw this can have a detrimental effect on regional long haul operations however I digress !
The best way of getting a competitive fare at short notice is indeed via those same consolidators and by being very flexible on routings and carrier combinations
Quite likely some of the most competitive will be cross and no alliance combinations and via some of the smaller hubs and indeed when going down under in particular 2 plus stops .
Now to the basic question , right across the transport industry ticket price buckets are designed to extract as much cash as possible based on demand and using some quite complex algorithms.
The most competitive ( queue cheapest in the main) tend to be available around 4 to 6 weeks out from departure. Book in advance of that and as the flight date closes in you will almost certainly pay more in most cases.
Add in seasonality and short notice and you must expect to be paying a significant penalty for your journey whether with a flexible fares operator or one of the legacy carriers. Indeed in all honesty close in the legacies are often much better value !
Your flexibility is considered worthy of a premium to any and all transport operators period.