Landed cost to be distributed among other Invoice items according to Quantity - SAP ByD

Hi Experts,

I have a question regarding Cost Distribution in Invoice, following the steps of "Unplanned landed cost in Business ByDesign" mentioned in this link: https://blogs.sap.com/2015/03/06/unplanned-landed-costs-in-business-bydesign/

First, I have posted a Supplier Invoice (1st Invoice) with 2 lines as follows:

- Item 1:

Qty: 3 - Unit price: 20.000 - Total: 60.000

- Item 2:

Qty: 2 - Unit price: 10.000 - Total: 20.000

Second, I create another manual Supplier Invoice without Purchase Order (2nd Invoice) to distribute Customs amount within items in the 1st Invoice. Steps as follows:

- Input the Description as "Customs" and select its item type "Additional Cost Debit Item"

- Input the Net Amount and in Cost Distribution tab, select "Distribute among other invoices or credit memos"

- In the pop-up screen, select the 1st Invoice in box "Invoice ID" (which is 47 in the picture) to distribute the Customs amount among its 2 items.

==> As shown in the picture, the amount is allocated among 2 items as regards the percentage of Net Amount (which is 60.000/20.000 --> 75%/25%), does anyone know the configuration that allows distribution according to Quantity (which then maybe 3/2 --> 60%/40%)?

I would appreciate it to receive your help. Many thanks.