Frimmel has it exactly right. I’m not saying there is any reality to the situation, just describing how the rules work. If you’re looking for reality, play something else. This is a board game designed much more for playability than historical reality. For example, how likely is it that in every battle, units die in the order chosen by the attacker or defender. All the infantry dies before the artillery before the tanks before the fighters. Or that transports, submarines, destroyers and fighters all die before the aircraft carriers and battleships. How realistic is that?
Like I said, if you’re looking for realism, you’re looking in the wrong place.
As for the Sumatra and Java convoy routes, just because they are labelled below the islands, don’t assume that is where the convoy route is located. Capturing the convoy route implies control of the entire sea zone in which the convoy route is located. Therefore, all “traffic” to and from the island is interdicted.
As for all of your rule changes. You are no longer playing A&A Pacific. You are just using the A&A Pacific board to play some other game that you have made up. That’s fine, as I understand from your comments on the Harris Game design board why you are doing this, but don’t take issue with those of us who play the game for the sake of enjoyment and choose to learn our history from books.
SS