Multiple modifiers getting applied to sales order line, while requirement is to apply only one

two discount modifiers created in oracle r12 with 10% and 15% respectively. both are included in level 1 incompatibility group. precedence is set as 300 for 10% and 315 for 15%. according to oracle, the lower precedence should be given priority inside the incompatibility group and thus 10% discount should be applied to the order line. But sales order line gets 15% discount applied no matter what. why is this happening ? what can I do resolve this issue ?