Display Discounted Value

This is a fantastic module, works well, but I've come across a tiny hiccup in the presentation of data that I was expecting and I'm not convinced it's not merely a user error.

Unit prices entered into the price table are substituted for base price, which is fine for the total price calculation; however it doesn't seem that the difference in price is passed as a discount for display.

Is there a way to append discount calculation in the rule that overrides the price, have I configured my price tables incorrectly and I'm experiencing a bug, or is it merely a substitution and there is no discounted price calculation since no calculation takes place?