This is not correct. As Lee already stated this value is locked in the dll files. All CITY_MIN_RANGE does is set the minimum distance cities can be from each other. CITY_MAX_BUY_PLOT_RANGE seems like it could be tied to the workable tile range, but again because the workable tile range is hardcoded, changing this value is meaningless. In fact, iirc any change of this value is ignored for purchasing as well.