The Raw Luck theorum. (How to make luck, like you make Units)
I think the idea of smaller forces being effective against an attack is probably most valid when thinking about the USA navy in both the Atlantic and pacific. Having say three small navies in a “V” formation gives then the advantage of options should one be attacked, while having one large navy would be a stalemate for the most part in the Pacific and usually a loss there. In the atlantic it gives the Axis something to worry about, where a UK fleet parked in one zone can be dealt with quickly and decicivly an multi-zone fleet makes you wonder what he’s up to. Just look at all the resources needed by Germany R1 vs UK, and this is a relatively small fleet compared to what USA can produce.
Good points Gargantua.