i have material which is called "Y31003", item model group settings for this item as below:
- Physical negative inventory : False
- Financial negative inventory : True
- Include Physical value : False

I placed a purchase order on 8/27/2014. unit price = 4.4(17% tax included) , Quantity = 75. the purchase order is only physical received.
(75 X 4.4) / ( 1 + 17%) = 282.05 (physical cost amount)
282.05 / 75 = 3.76 (unit cost price)
Since i didn't select the "Include Physical Value" in the item model group and also not configure the cost for the item, the cost of this item is Zero when it was used by production.
From 9/3/2014 to 9/19/2014, 20 item(Y31003) was used for production purpose, and the production order is also ended. which means this item is financially issued with the cost of Zero. now the on-hand inventory is 75 - 20 = 55. the unit cost price in the system displayed as (282.05 / 55 = 5.13) which is wrong as below:

Now i want to change the settings for this item by enabling the "Include physical value". Even though the purchase order is not financially received, i also want the cost price displayed as close to the actual cost as possible.
Question:
How to adjust the item cost price to the actual physical cost price(3.76) by not closing the inventory ?
Many thanks.