i think predicted ATAR is an internal process for schools where they base scaling off how the cohort performed.
The only time WACE performance in the previous year is relevant is when they chuck your aggregate into the TISC calculator to get your ATAR.
can vouch for this bc I always check my aggregate and ATAR with the TISC calculator.
But the school always robs me of at least 1 point on both occasions I swear