Problem on Tolerance Key SE Max cash discount deduction

Hi Gurus!

               I am facing the below problem,help me to sort out

I already set the configuration for SE Tolerance key,tolerance limits are Upper limit=10%,Lower limit=5%,as well as i defined the attributes of messages as Warning if it exceeds the above Tolerance limits.

Now i have done a PO with Max.cash discount 3%.In this case System has to through warning message,but it accepts the Cash discount 3%.

How to get the warning the message if the tolerance limits exceeds?

Regards,

Vinoth