Of course if UberJJK wants to tell me I'm crazy about the economy of scale thing, he'd know better. I know I at least effed up the terminology.
You are mostly right.
Economies of Scale do technically reduce the unit cost since overhead is spread over the number of units produced. And it can also reduce the variable cost to a point since materials are generally cheaper the more you buy.
Now while the following explanation does overlap with yours a lot it's probably easier to follow:
Costs are broken up into two variable and fixed costs.
Fixed costs (also called Overhead) are, as their name implies, fixed payments you have to make irregardless of production. Rent for example. Electricity often finds itself here even though it's technically fixed and variable. Things like depreciation also go here but that can get
really complicated and we fortunately aren't worrying about that in this quest.
Variable costs are, again as the name implies, dependent upon the number of units produced. Theoretically if you produce nothing your variable costs should be zero. However this doesn't only cover the materials it also covers the Direct Labor. The details of what is and isn't covered however is complicated enough that I'm not going to try and explain them.
Lets take the Arc Reactor for an example. During 2173-Q2 we had an overhead of 87,005,000 credits. That's because all the expenses listed in the expense section of the P&L are things we'd have to pay irregardless of our production.
The Arc Reactor itself has a variable cost of 50,000 credits.
Tthe formula for determining the average unit cost is:
C = V + F/N
Where V is the variable costs, F is the fixed costs and N is the number of units produced.
Continuing the example during 2173-Q2 PI produced 61,000 Arc Reactors therefore the cost per unit is (theoretically):
C = 50,000 + 87,005,000/61,000 = 50,000 + 1,426.31 = 51,426.31cr
Now in reality it's a lot more complicated since your pretty much never producing just one product, although in the example year we did, and there are all sorts of complicates associated with determining how Overhead is assigned, although we could easily do it based off the production spent on that line, but this is a brief overview.
So yeah as I said your mostly right.