Hi,
You can meet your requirement by Absence Valuation Rule...
Create a Valuation Rule
Assign it to Unpaid Leave (Absence Type)
Create a Wage Type (in IT0014)
Set Counting Class
Attache Wage type with Counting Class, and assign percentage as 100%
Enter a monthly wage type amount in IT0014
Finally for any unpaid absence for a month entered in IT2001.. the amount will get prorated accordingly.
This should sort your issue..
Regards,
Veeram