cycle count of inventory with lotwise FIFO cost rules

I want to maintain FIFO cost method for spare parts of maintenance inventory. Also, need to setup the process for the cycle count.

Now, I have two lots with respective cost:

Lot 1 – qty 5 – cost @ 100 USD

Lot 2 – qty 7 – cost @ 150 USD.

 

Now, the total inventory in system is 12. And at the time of cycle count, the physical inventory is found one short as 11.

 

During cycle count, user has to enter the physical quantities lot-wise. Physically, user does not keep the inventory lot-wise, the inventory is mixed in warehouse. So, against which lot, the user should mention the quantity as short/ less? This is important because the cost of both the lots is different