FIT calculation for employees paid 10 months in a year

Summary:

Is there a note on how Oracle calculates FIT? We have employees who only work 10 months(June & July skipped) as part of the school Calendar, but Oracle calculates FIT as if the employees are paid for the whole year.

Content (please ensure you mask any confidential information):

We have employees who work either 10, 11 or 12 months in a year depending on a Job Classification.

If we create multiple Monthly salary basis with annualization factor as 10, 11 & 12, the Annualized salary stored in the system is correct. But the Tax(FIT) calculation for the 10 & 11 months employees isn't correct. Oracle is calculating the FIT as if the employee will receive 12 months of Pay.