Does your school rank actually affect your atar mark or your cohort?? My school legit averages 2-3 b6
school rank is just an indicator of how strong a cohort from said school performs on average because [generally] it's consistent especially for the top 100. for example the top 10 generally have strong cohorts (those tend to be selective schools or elite private schools which already start off with generally academic cohorts anyway), so a rank in the top 10 indicates that the cohorts are generally strong and most of the student cohort will at least get 1 band 6
school rank doesn't really affect your atar, but if you're not ranked 1st (where your cohort has no impact on your marks) or close to 1st for your subjects depending on how many b6s your cohort generally gets you can get fucked over by the strength (or lack thereof) of your cohort
for a school like yours you should just aim to be 1st in all your subjects so your cohort doesn't impact you in any way