Attached is a table showing the logic behind the way prices are calculated on a sale in Infusion.
Contract Rates of the types Fixed Rate or % Above Cost always take precedence over other price rules - even if there is a better price in the product for that (Promo/QtyBreak).
Contract Rates of the type % Below Selling Price are effectively a contracted discount. This contracted discount is applied to the standard rate of any price level, or to the quantity break of any price level. It is also applied on top of rates calculated using the discount matrix. This contracted discount also trumps the Customer Default Discount - no matter if the resulting rate is not the best for that customer. The only exceptions to this type of contract rate are if there is an active Promo Price or if the product in question does not allow discounts.