Just going to add that if you aren't rank one though, you may still be affected. From the perspective of a weak cohort, if and only if you are rank one, you won't be affected by cohort performance.
Then again, if you're ranking is below a classmate's they should perform similarly come exam time, unless SACs were performed under shady circumstances (e.g. when teachers recycle SACs from previous years, and some students who bought notes from past year 12s get an unfair advantage :/ )
if you want more examples/proof/reassurance chuck me a pm. I know cohort strength can be really concerning, especially in a weak cohort, but from a objective perspective (i.e. less motivated cohort, less resources etc), if you are rank 1 and get an exam score indicative of a 50, you will get a 50.
(unrelatedish- this is why HSC in QLD is dodgy)