Please see below steps in order to show the Current Average Cost using formula on the Inventory Valuation Report:
--Navigate to Reports > Inventory/Items > Inventory Valuation > Customize Summary:
1. Go to Edit Columns tab
2. On the Add Fields section > Click Add Formula Field
3. On the Formula Type > set to Ration x/y
- X = Inv. Value
- Y = On Hand
- Rename the Column Label as "Average Cost"
4. Click Preview
Result: You will now be able to see the current average cost for all the locations of your items.
When MLI is on, average cost is displayed only for the item's preferred location. If there is no preferred location defined for an item, the average cost displayed on the report is blank or zero.
Enhancement request was already filed to address this concern under Issue # 156866.