Shared religion bonus?

Does anyone understand the mechanics behind the shared religion bonus for tourism? I assume it benefits diplomacy as well. Trouble is, in my current game as Portugal founding Catholicism I've converted all of the Netherlands and the majority of Carthage to my faith. Neither of them even founded pantheons. Yet while I could have sworn at one point I got the bonus with both of them, I looked again a hundred years later and have shared religion with neither. This is despite the Netherlands being geographically isolated and Catholicism is the only religion there. Amsterdam, for instance, is size 19 with 15 followers. The other cities have a higher ratio.

Is this a bug? How do I get the shared religion bonus?

I believe you get the bonus religion stuff if they have a majorit of CITIES following your religino, you sure that they don't have cities in Fog of War?

OK thanks, that makes sense for Carthage as she has some small cities that are not Catholic. William has at most 1 or 2 cities in the fog but 9 Catholic ones in the open.

The odd thing is, I just looked again a few turns later and got the bonus back with William. Nothing changed in the mean time in terms of his number of cities or how many were Catholic. The only thing that happened is he picked a different ideology when I looked last and only now I see the 34% penalty. Maybe it took a few turns for the game to adjust? Has anyone else experienced this?

Thanks for the info.