rescheduling horizon

Hi,

I am looking at MD05 and see a new purchase req being created when I have a shipping notification due. I was expecting the system to propose a reschedule in message of 10 against the shipping notification and not create the purchase req at all as the shipping notification is in the rescheduling horizon (PDT 112 days + GR Processing time 4 days + purchasing processing time 2 days + rescheduling horizon 60 days). But instead the system gives me a 20 message for the ship notification and a 30 for the preq. Can someone explain to me why the system is doing this ?

The rescheduling horizon is 60 days in config and the PDT for this externally procured part is 112 days from the PIR. The MRP type is PD. The GR processing time is 4 days and the purchasing processing time is 2 days. Below are the screen prints.

Thanks