i really don't know who coded the AI behaviour for the civ2 engine, but the AI lacks of that, enough "artificial intelligence" .
i read somewhere that the AI was *originally* programmed to work on map ranges of NO MORE THAN 10000 tiles (75*120 map size or any other size that do not overpass the 10000 tiles). that's the reason you only can build maps of that size in the mapeditor or when you start a new civ2game. there is a relationship between the number of tiles and how the AI should/must work on them. currently we build gigamaps, that allow you to create surfaces up to 32000 tiles!!!!. so as you imagine the AI is trying to "understand" something that is over the default limit.
i think, that if you want to build scens in SP you should use no more than 10000 tiles. if you want them for MP, then there is no problem for obvious reasons!!!