That´s the genius of Antal1987, not mine.
It´s too early to give here a full résumé about the Antal1987-4 patch, but as you can see I´m now in the testgame at the border to era 4 and there were no incidents. One tester showed a save game where one of the citizens couldn´t be replaced in the city. screen. If this has to do with the Antal1987-4 patch is not proved. When playing with that patch, I think there should be the "houserule", that no combat settlers should be allowed, settling one tile next to an enemy city (especially with barracks inside that new city) .In my eyes this could be the reason, why Firaxis set a two tile distance between cities.
The Antal1987-4 patch also fixes the scientific golden age and some graphical glitches in the civilopedia. That patch doesn´t boost the limit of the city tiles that can be used by city laborers ( that is a function of later patches of the Antal1987 framework), otherwise most industrial and modern units would have needed a complete revision of their production costs, exceeding the limits of the Firaxis editors (and my free time).
I think the future download of CCM2 will include that patch and a note how to use it, but the tests are still running. You can find the Antal patch frame work here:
https://forums.civfanatics.com/threads/useful-patches-for-civ-3-conquests-v1-22.526285/