Another way of explaining it is to realise that the places are allocated from the top ATARs down so the 99.95 are allocated to their first preference.
Then the 99.9s are allocated.
So assume that one course is really popular with only 50 places and that 50 or the students with ATAR's of 99.9 or 99.95 apply for that course then the cut-off is 99.9.
So if a student with an ATAR of 99.6 also wanted that course they are out of luck as all the places have been filled. When UAC gets that that student they ignore their first preference simply because that is no longer available and treat their 2nd preference as their 1st and allocate them to the course they have as their second preference, assuming that their are vacancies in that course.
If a person's first preference is full UAC gives them their second. If their first five preferences are all full when UAC reach their ATAR they will allocate them to their 6th.
Then the 99.9s are allocated.
So assume that one course is really popular with only 50 places and that 50 or the students with ATAR's of 99.9 or 99.95 apply for that course then the cut-off is 99.9.
So if a student with an ATAR of 99.6 also wanted that course they are out of luck as all the places have been filled. When UAC gets that that student they ignore their first preference simply because that is no longer available and treat their 2nd preference as their 1st and allocate them to the course they have as their second preference, assuming that their are vacancies in that course.
If a person's first preference is full UAC gives them their second. If their first five preferences are all full when UAC reach their ATAR they will allocate them to their 6th.