Partial Clearing in F-54

Hi,

Advance Amount is Rs. 1000 & TDS on that is Rs.100

Invoice is rs.5000 & TDS on that is  rs. 500

Now i am Clearing in F-54

If we adjust the total Advance Rs 1000 against invoice rs. 5000 then system cancel the TDS on Advance rs.100

If we adjust the Partial Amount ie, Out of total advance rs.1000 if we adjust only rs.700 then how TDS reverse. we are not getting the TDS proportionately. How we get the Proportionate one.