I was designing a car, and it had some rather (intentionally) silly engine requirements for the scenario, and I made the engine as big as I could, and fitted a huge turbo to it, and it didn’t fit into the car. This in itself is not a problem - the problem is that it took me a while to work out that the size of the turbo was being added to the size of my engine, and I found myself reverting to a rather painful process of shuttling through all of the engine design screens as I used trial and error to work out what was going on.
It seems to me that the least painful way to change this painful experience would be to show the engine size in the statistics for every part of the engine that impacts the engine size, when you’re designing that part.