You can tweak the available options in "Caveman2Cosmos\Assets\Config\RoMSettings.xml" under MinCityDistanceQuestion...is there any way in BUG to change the Minimum City Distance to 1, please? In game, all I get is 2 to 6. Can't find it in any of the BUG xml files, as well.
Thanks!
Having cities neighbouring other cities on adjacent tiles is really not recommended.