The projected acceptance rates are derived from the Projection targets. For Freshman you take the FTF target # for the specific major multiply by 3 (projected 33% yield but could be different for each major) and divide by FTF Apps x100 to get acceptance rate.
Again all these are projections so they will fluctuate from year to year.
https://content-calpoly-edu.s3.amazonaws.com/ir/1/images/2019-20%20Enrollment%20Projections%20for%20Continuing%20Students%20-%20no%20total%20error%20adj.pdf