Yes your atar can be higher, but it would be difficult (but not unusual) for your HSC mark to be higher than them. For example I was ranked in the bottom half of my cohort for every subject I did, without fail. 6/8 MX1, 3/4 MX2, 17/31 EngAdv, 6/11 Geog and 4/6 Physics, but then I still managed...