Planning strategy 40

Hi,

I am testing planning strategy 40 and here is the scenario

Avl Stock 200 GAL

PIR: 300 GAL

Sales Order: 600 GAL

When I ran the MRP the system proposed a planned order for 400 GAL and the entire PIR gets consumed by the sales order. I am trying to understand how it came up with the planned order qty and I was expecting a higher qty. The 400 will meet only the sales order req along with the existing stock so how about the PIR requirement?

Thanks

Sachin