About right I would say Comp Stall. Without working out the initial and final great circle tracks and using the formula for the convergence of the meridians to give an approximate value of track change it comes out as follows:-
Since I do not have the exact Lat/Longs of CS and MLY near at hand I have used CS and BN with off the top of my head figures.
Cairns 17.00 South 145.00 East
Brisbane 27.30 South 153.15 East
Change of Longitude is 8.15
Mid Latitude is 22.15 South
Convergency = Change Long times Cos Mid Lat
= 8.15 * Cos 22.15
= 7.38 approx
Someone may have more accurate data but the above suffices. The trip distance is not the main variable if there is no Change in Longitude such as Directly North/ South tracks then there is no convergency as you are tracking along a meridian. Greatest convergency and hence track change occurs on East/ West tracks at higher Latitudes.