It's funny you would mention that. I would really really like to add that to this mod. Unfortunately it isn't possible. I can change the value but the game has it's own cached value that it uses. It just ignores mine.
I created a separate mod for my own use that increases the MIN_CITY_RANGE value by one so that the cities are spaced out farther. That's the only way I play the game now - it's awesome. Unfortunately this can't be done to in the Advanced Setup screen. It has to be done when the game is loaded so the change is a constant value for a given mod. I assume there are already some mods like this. If you look around you can probably find something. If not - let me know. I could make a couple of quick mods with each one having a hard coded city range.