Applying Quantity Discounts

I am learning how to use the various discount options in Retail for Dynamics AX 2012 R3 (6.3.124.0). I set up a quantity discount with the idea of if you buy five items from a category then a 10% discount is added to all items from that category on the order.

However, when I do this it only applies the discount to items after item 4. Am I misunderstanding the functionality of the quantity discounts? If so, any advice on how to set up a discount for this scenario? 

Thanks,

J.M.