Discount Sales Price is setup in the Customer form > Pricing field.
The Discount set in the above form will show in the Disc field, Price field will show the item’s Sales Price.
In cases where there is Category Discount, the best/higher discount will be taken.
It is the Category Pricing discount that has higher discount so that is used as Invoice discount.
It is the Customer > Detail tab > Pricing > Discount Sales Price that has higher discount so that is used as Invoice discount.
Bug: 2874