We are experimenting with miscellaneous line charges at the moment. We’ve noticed that if a customer has a discount applied to them, a miscellaneous charge added to the line as a percent type uses the Gross extended amount to calculate the misc charge, rather than the net extended amount.

For example, a customer is given a 10% discount on all products. A line is entered on an order for 10 each of an item at $10 apiece, for an extended price of $100. The system will calculate a 10% discount, or $10. So the line has a gross extended amount of $100, discount of $10, with a Total (net) Price of $90.

A miscellaneous charge is added as a Percent type, with 8% being the percentage. When the system calculates the amount of the misc charge, it uses the $100 (gross extended price) instead of the $90 (net extended price), and the charge calculates as $8 instead of $7.20.

What is the business logic supposed to be doing, and is it configurable anywhere? Ideally, we want the percentage miscellaneous charge calculated against the NET price, not the GROSS price.

Any input would be much appreciated.