Free Goods quantity to be proportionate to main item quantity

Dear Sirs,

I am new here. Need your guidance.

My issue is if I change main item quantity manually in VL01N, the free goods quantity does not change automatically in proportion to the main item quantity.

I have maintained 1 as Calculate Rule and E as FG Delivery Quantity, in T Code -VBN1

The conversion factor is 5 m3 (Main Item)= 1 EA (Free Goods) In sale order qty = 10 m3 (Main Item) = 2 EA (Free Goods)

But if I change the main item quantity from 10 to 5 and press Enter, the free good quantity is not automatically changing to 1, which it should be. My requirement is system should change the free good quantity automatically in proportion to main item quantity.

Thanks & Regards,

Sneha Todankar