At unsw it is uncapped as in everyone can get a hd if they do well enough
Actually it depends on the course you are doing, some courses at UNSW is moderated, from my experience with law subjects, all subjects are moderated on a normal distribution curve, essentially means often the mark you get is moderated for each assessment task against how well your peers is performing, this makes sure that the grade you get is reflective of your position in the cohort, i.e. high distinction is the top 15%... (but in reality in law it is actually even less than that)
Other courses may be uncapped, it is best to ask your faculty coordinator for what the marking for each courses are like or the course convenor of each course.