Formula for unit cost derivation in FIFO

How is the unit cost derived for any item in FIFO at the time of accounting. Users need a report reflecting the exact unit cost that will be applied on any transaction or was applied on any transaction using FIFO Costing Method.

The costs in history table do not tell the exact unit cost that is going to be applied on a transaction. System calculates the cost based on all existing layers quantity and unit costs when the Layer Cost Worker runs. How to fetch the cost prior to Layer Cost Worker's run?

Or is there a setup which will force the system to pick the unit cost of the most recent previous layer?