ASCP - Logic for deriving new_schedule_date in Constraint plan

Hello Folks
In an ASCP Constrained ( Enforce demand due dates) plan should new_schedule_date always be the same as Need By Date. I have a situation, where new_schedule_date for items are pushed out by a week.
Any pointers would be appreciated.

FYI, MSC: Purchase Order Dock Date Calculation Preference is set as promise_date and promise_date for the item(post plan run) is NULL.

Thanks
Mayank