You are indeed correct! I was thinking of this problem in terms of the territories I've actually visited... turns out GIB is approximately as far as the closest point of Britain itself, but Jersey is a good 120km closer!
OTOH, if you're stuck in San Marino, a country which is technically not in Schengen even though it has open borders with Schengen, and is thus not covered by the President's proclamation even though it has one of the world's highest rates of coronavirus infection per capita... you can easily manage the 150km over to Croatia (part of the EU, but not yet Schengen, and thus excluded as well) via helicopter. Same if you're a Catholic official and haven't left the borders of the Vatican...