Strasbourg in France should also make a dent into France's contributions then. Would be nice to know how much it would be, without those things calculated in - sure they are?
Host important EU institutions that cost a fuckton, having a world harbor (which is a boon for all of Europe being so central to it all), etc, while themselves being small.
Belgium would need to put in like 7x more per capita what Germany does, simply to be at parity.