Availability check not considering open purchase order qty in case of shortage of available stock

Dear All,

I have 975 pcs as available stock (unrestricted), on booking sales order of 1000 pcs, availability check confirms only 975 pieces though i have open purchase orders having quantity more than 300 pcs. So i want that system should pick the balance 25 pcs from those open purchase orders. I have done changes in configuration through OPJJ whose screenshot is attached herewith. Pls tell, is there any changes required in configuration or is there anything which i can do in configuration so that i can get the desired result.

Regards

Deven