I have a question regarding to the calculation of annual leave, not sure if this is the correct place to put this query

A client of mine closes his factory for 4 weeks in December, the staff's employment contracts all indicate that annual is 4 weeks per annum. They are using Pastel Payroll and are currently accruing leave at the rate of 1.25 days per month. This equates to 15 leave days per annum and results in the leave days due on payslips generally reflecting a negative value. When I asked the bookkeeper about this, she stated that they track leave days on a spreadsheet, now this is all well and good by my reckoning until such time that you terminate an employee from your system, surely the correct method would be to change the 1.25 days to the correct number of days that the employee does receive in order to keep an accurate record and alleviate any issues on termination?

I am not that clued on Pastel Payroll and would like to know whether you can change the allowed number of leave days or whether it defaults to 1.25 days per annum, and whether the system would in fact deduct negative leave days from the final calculation if you terminate an employee from the system?

Thanks