CTM - Safety days' supply

Dear All,

I am doing CTM run with backward scheduling strategy. In the CTM profile, I have checked "Consider Safety Days' Supply" and defined the value of safety days supply in the location product master. After CTM run, as per the expectation, the PReq (purchase requisition) should be created earlier of the DepDmd (Dependent Demand) by the safety days supply. i.e. if safety days supply is 3 days and DepDmd is on 12th Dec then PReq should be created for 9th Dec. However, the safety days's supply is being ignored and the PReq is being generated for 12th Dec only. Can anybody help me? Its very urgent.

Thanks in advance

Ehsan Ahmed