Instead of naval invasions be an all or nothing event I would like to see them be done with a gradually accumulating investment scaled to the territory value. So to invade tiny island like Midway might cost 2 million while invading a value 12 territory like Sicily or British Columbia might be 250 million. This investment should build up gradually following a poison distribution centered at half your naval score in the area (so basically you simulate flipping a coin for every point of naval score and count how many heads you get), this amount invested should be reduced by a poison distribution centered at three quarters of your opponent's naval score in the area (so the defending forces count 50% more). Once the invasion force has been prepared, the player can trigger the invasion at any time they want however every turn of delay costs 5% of the total amount. The Japanese would have the power to prepare invasions during peacetime (and only pay half of the delay cost during peacetime). It would be possible but very expensive to replicate things like Operation Husky. However it would require a great deal of naval supremacy so it would be very difficult to pull off the hypothetical British invasion of East Prussia and invading Vancouver isn't possible unless you deploy a battleship fleet to the Pacific.
There would still be randomness but it wouldn't feel so bad when you dont get an invasion, at least you are saving money.
"The real world figures are contaminated by real world events."