P4312 Purchase order Partial Receipt question

  I have entered an OS purchase order with a quantity of 1 ,amount of 30,000.00.  Is there a way to recieve this in 3 amounts as invoiced ;15,000. , 7500.,7500.

 If I try to receive it in the P4312 when I change the first amount from 30,000 to 15,000.and receive the whole amount gets received.

I can receive partial amounts if I change the quantity to a  a figure of less than 1 i.e .25 .30 -quite normally.

Is this the only way to handle this kind of partial receipt? Is it possible to leave the quantity as 1 and still receive partial amounts? is there a Processing Option that can be set on the P4312 to do this?