Adjustment amount (set amount) is calculated first against total amount/fees, THEN Discount is applied against all including amount minus adjustment. When both are used in conjunction, this creates inaccuracy with how the percentage of fees discounted is displayed on the invoice, especially when applied to fees only.
A invoice is set to $500 Expenses + $500 Fees. I have $100 in adjustments, and 10% off in Discount - both set to Fees Only. This, on the invoice, displays as $500 in fees, and the 10% discount of those fees totaling $40, which is inaccurate.