Guantanamo is leased land. Cuba never cashes the check, but every year one is sent. So, it is still sovereign territory of the nation of Cuba, leased by another country.
They could cash the check it still wouldn't be a border. The US just rent a place according to an old contract Cuba no longer recognizes. It's just a case of a landlord wanting the guy out and Guantanamo Bay isn't a US territory. It's just a military base on foreign soil like the US hold others around the world.
Cyprus is 9250 sq km. I'm not sure what position it'd be in if this list was extended, but I think there would be a few more Pacific Island nations above it, due to them having loads and loads of small islands.
- Indonesia / UK / PNG / ...
So not really