We have an in-school one where the most ranks first are taken into account as well as ranks 2 and 3. We have this for a "top 10"
BUT
The school can pick out the classes where the smarter people are (obvi the people ranking first in a few things, second in a couple others are going to be first, BUT the people ranking 4th in this subject would be more-likely to get a higher ATAR than people ranking 2nd in a subject with no strong competition).
So basically we have one after ATARs on how good your ATAR was, and one before HSC exams based on ATAR-predictions, but the school only gives ATAR predictions to people who are high achievers and explicitly ask for one (e.g. for med entry).
Fun fact, my school screwed up the in-school method my year. Ranking my friend 2nd with a 98.5ish estimate (1st in Physics, English (Standard), PDHPE, and Catholic Studies (non-ATAR lol))
He got ~89.
~lol~