Payable Payment Term Discounts

Hello payable experts, I am trying to use discount feature on payable payment term. I defined 1st, 2nd and 3rd discount as 50 % 30% and 20% on 7 days, 15 days as 20 day. And this is rightly reflecting on Invoice payment schedules but however when finally I am making payment by PPR, it is taking maximum discount i.e. 50% in all cases even if the Invoice data have crossed 7 days. Any pointers will be helpful ? Does it have to do anything with "Always Take Discount" option at Supplier level/ site level and Payable options level ? Thanks, Viren