Culture Experts Explains this:

[obsolete]

Why is my inner ring weaker than my outer ring?

 

[Joshua368]

I'm no culture expert by any means, but would Joao's culture have expanded to the outer ring yet?

 

[Korias]

Moreover, why wouldnt Darius's culture overpowered you? The capital is right there, and yet you still have territory next to it.

 

[Solomwi]

Is Darius your vassal? I'm too tired to crunch the possible numbers, but the first thing that occurs to me is that it's actually his culture winning out in the outer ring, with the result that you get the tiles by virtue of being the master. That's not as satisfactory an explanation for the tiles toward Guimaraes as it is for those toward Persepolis, and less still for the inner ring itself, but maybe it's a step in the right direction.

 

[obsolete]

Yes, I just vassaled him and that's why the domination kicked in.

Also, the city USED to be his.

 

[DonaldAtHome]

Each tile has a control rating like: DietyBS 74% / Joao 26%. If Joao just took the city and came out of disorder, his new city probably has not over come the control threshold yet. The purple tiles are probably DietyBS 51% / Joao 49%.

 

[Solomwi]

Each tile has a control rating like: DietyBS 74% / Joao 26%. If Joao just took the city and came out of disorder, his new city probably has not over come the control threshold yet. The purple tiles are probably DietyBS 51% / Joao 49%.

That's obsolete's city, not Joao's. The border around the city tile is hard to see, but it's there. If Joao never controlled Susa, I only see one Portuguese city, Guimaraes, that can put culture on the hill 7 of Susa, and that hill's in the outermost ring of Guimaraes, while being in ring 2 (of 5) for both Persepolis and Susa, so it should still be swamped with Persian culture, and therefore be purple, since Darius vassalized to obsolete. I'm not one to cry "bug" quickly, but that tile in particular makes me think there may be one here. The culture accumulator seems to be accounting for Persian culture in the outer ring, but not the inner. All of the inner ring tiles except, I think, the wine 3 of Susa are still within the cultural radius of at least one of Darius' cities.

 

[r_rolo1]

The city was gifted right? That might explain it

 

[TheMeInTeam]

Any tile that would be darius' in your bfc will be yours by virtue of master/vassal mechanics.

Any tiles that wouldn't be darius' would go through normal checks for ownership. Perhaps Joao built enough culture in his inner ring (which gets a bonus) while in possession of the city for his culture to be stronger there, while weaker in the outer ring.

This scenario is pretty rare.