What's Cost Per Unit Key Figure?

Hi Gurus,

We thought that Cost Per Unit was the cost of holding inventory in the concrete location, but before some testing we can't see that.

That's our Key figure definition

1- What is Cost Per unit?

2- Cost Per Unit value is recalculated by Profit Optimization Process even if we update the Key figure manually?
3- If Cost Per Unit depends of Dependent Demand, (Which is a calculated Key Figure) How can we define Cost Per Unit?

4- Where can we define Inventory Holding Cost.

Many thanks in advance!