And his scale may(?) be more based on movement/production rates rather than speed of play.
This makes common sense. I discussed this issue with Larry, and will edit in a link later. But the importent here is the production rate. The ship movement dont fit into this, because it took 12 days to cross the Atlantic, not 3 months.
When it comes to speed of play, as you put it, that is very a difficult issue. In the 1939 startline we had no guarantee that WW II would go on for 5 years. If UK, France, USA and Russia had attacked Germany in 1939, then the war would have lasted 1 year, because of an alternate decision. If Hitler had not done all his mistakes, the war might have lasted for 10 years. Just look at the Vietnam war, that lastet for 20 years, in one tiny territory. And the Iraq war 1990 lastet 100 days. The speed of production are fixed, the speed of movement and play are not.