First of all, I would like to thank you for your help and time!

Now, regarding the items...

The items are (as you correctly stated) situated in the various locations in the beginning.

We should also treat the items as "unique" post parcels. Allow me to explain:

If you have an order (in the input delivery list) stating "An item has to be moved from location #2 to location #3" then,
once you push this item in your LIFO list it should be treated like a "unique" parcel that has to be delivered to location #3.
Other items may be pushed on top of it, but ultimately this specific parcel will have to be delivered to its target location.

I assume that this constriction will influence the cost we pay to load-unload items in order to unload a specific item:
If it is above most, the cost (1 point per load-unload) will be smaller...

Sorry if I am a bit confusing, I'm trying my best to explain a not-so-well stated problem

And again, thanks for your time