I thought geography scaled higher?
http://www.uac.edu.au/documents/atar/2016-ScalingReport.pdf
Go to page 35/36 of the report and look at the mean scaled mark, Ancient has 24, Geography has 25.5, the higher the number from 25 (since 25 is average), the better scaling the subject has
But in saying that there's 10000 ancient kids but only 4200 geography kids so I guess it does kinda explain geo's higher scaling, sometimes less students means less standard deviation and spread of marks