Hours calculation of Basic salary

Dears,

Kindly i have an issue that i need a help on it as follow:

- in the company setup i set that the standard working hour per day is 8 Hours and the hours per standard year 2880

- in the Payroll ID i marked the Auto pay flag

- i have a monthly master pay cycle where i set the ending date is 25 of the month

- in the PO of R07200 i set 1 in the option of "Auto pay Proration"

so what i am facing now if an employee is hired at 30 of July and while running the payroll of August which start from 26-7 to 25-8 i found that the system is calculating the hours of the Basic Salary (Pay type 1) 205.78 so does anyone have any idea about how the system is calculation the hours in this case ??