Razor,
Nice try :-D I was thinking it was probably something they discovered in playtesting. But I just can’t think of a reason to differentiate between islands and continents for this purpose. I know, for instance, that the Italians had a pretty good navy. Their surface ships were mostly well-designed and fast. They did not, however, equip them with sufficient anti-aircraft capability. They didn’t have any aircraft carriers of their own, which forced them to hug the coastlines whenever possible in order to stay within range of land-based air. With the current rules, they could be protected by an airbase in, say, Sicily. But if they were in the Adriatic they’d have no defensive air cover, even if they had airbases in both Yugoslavia and Italy.