Issue in individual planned order creation in STO scenario

Hi All,

I will explain you my scenario first.

This is a repetitive and MTS scenario. I am having 3 plants A, B and C. B and C are ware houses and A is a manufacturing plant. X material is maintained in all the 3 plants and a special procurement key is maintained in B & C which says that part to be procured from plant A (that means to be manufactured in plant A). Lot size is MB in B & C and EX in A, MRP type is PD in all. No min lot size max lot size, rounding are maintained

After getting sale orders in B & C, when MRP is run system is creating a PR in B & C and planned order with ref to those PR's in plant A.

The issue comes now.

System is creating planned orders in A sometimes by combining both the demands and sometimes individually. Some times it will combine partial quantities from one sale order of B and one sale order of C and creating a planned order.

i am not able to understand on what basis it is combining the demands and creating planned orders. I want the system to create planned orders individually for each plants.

What settings/changes i need to do for achieving this. Please guide me.

Regards,

Krishna Chandra