If you have multiple services and/or discounts on an order and they are all set to a certain percentage, they will effectively "ignore" other services that are calculating a percent of your order or line item group. This is to avoid a never-ending loop with your services and discounts - if they were to interact with each other, the price of one would cause the other to increase, causing the other to increase, causing the... and so on!

Check out this article to learn more about excluding logistics, services, and rental items from discounts and fees.