Any airport to any airport. The route graph is not restricted to a region, and long-haul trips through a stopover hub are exactly the case the stopover engine was written for.
One honest caveat. The bag and seat fee estimates started from European carriers, because that is what the first user flies. They are estimates you can correct in Settings, and on a carrier outside that set they are more likely to be wrong. The fare itself comes from the same live search either way.