Changing amount of chemical used to coincide to "actual sprayed acres" and not Field acres

When entering new chemicals in the product details screen, I enter the amount of acres each jug does. When I enter an activity, the amount of product used is displayed based on the assigned acres to the given field regardless of the amount of acres I spray in the said given field. The sprayed acres change on every field depending on overlap. My field acres are based on actual GPS acres, not activity acres. There is a 5 to 10 percent difference when doing an activity vs GPS acres. The amount of product used in the top line should be based on the applied rate in the product details screen that is when I enter the product in the inputs screen X the acres that were sprayed. Currently, the total amount of product used in the activities screen is based on field acres and it does not change with sprayed acres for that particular activity. The only thing that changes is the bottom line which dilutes or increases strength with the acres sprayed. in the activities screen, The top line "amount" should be variable based on acres sprayed not fixed based on the field acres. The bottom line "amount used" should be fixed based on the amount of acres each jug sprayed, the volume of product in each jug and the actual acres that were sprayed.