Now, if I understand correctly the extra "circle" of squares becomes available to the city as soon as they're withing the culture borders, right? Would it be possible to modify it so that instead the city is required to be of certain size before it can work those tiles? Just seems to me that getting access to so many city tiles early on could be unbalancing, but if it can be set to, for example, only be accessible to cities of size 16 or more then it would make it easier to grow large cities without potentially unbalancing the early game.