Currently if we apply promo code during order creation in call center or applying promo code during order modification in call center, discount amount is getting applied under 'ChargePerLine', because of this discount amount is not excluding properly while order cancellation. Please find the detailed scenario below:

Promo code: $20 OFF on buying Item A, where Item A price is $150

Now CSR created order in call center for Item A with 3 quantity. As we have placed 3 quantity, discount will be 20 * 3 = $60 which is getting applied under 'ChargePerLine'

Line Total = $450
Discount = $60
Order Total = $390

Now, customer requests CSR has to cancel 1 quantity from the order and CSR proceeds cancelling 1 quantity

Now, Order Total should become $260 because ($150 * 2 = $300; discount is $40)
but as the discount is under 'ChargePerLine' order total is becoming $240 ($150 * 2 = $300; discount under ChargePerLine is $60)

As the discount is under 'ChargePerLine', proration is not happening properly.

Suppose, if the discount is under 'ChargePerUnit', then proration will happen properly

So, please provide an option to prorate discount under 'ChargePerUnit' and 'ChargePerLine'