From looking at the guide you get 7 "host social" just for hosting in the first place and then +2 (or 1, or 0, or -1) for each kingdom depending on your nation approval, and the total host social check is supposed to be 13 or higher - I don't have screenshots or exact number values or anything but four out of seven kingdoms were definitely at max approval (which should have meant +8) and I'm pretty sure all of them were past the halfway mark?
I also had 300+ likeability for the check beforehand, so ¯\_(ツ)_/¯