Well to be honest, it doesn't affect you at all, since that's last year's ranking, however it gives a good indication of how good your cohort is.
And rankings don't really mean anything, it's not like atar or anything, it's based on the number of band 6's. So an 88 or an 89 which is still an amazing mark, doesn't contribute to school rankings at all
However in saying that, you want your cohort to do as well as possible so your internal mark can be the best that they can be.
If you're ranked well though, then your cohort won't really affect you too much