[Ming]

I think the map used and whether score graphs are enabled are just as important as the difficulty level. The AI cannot judge the relative strategic importance of corner and border provinces and need a wrap-around map to be more competitive. For reasons discussed elsewhere in this Forum, turning on score graphs makes the game more challenging in the more difficult settings as the AI mistakenly see you as weak and will gang up on you.

I find the "Desert Eye" map with score graphs enabled and 12 impossible AIs to be the most challenging setting in SP(without going into any programming - as I cannot even do the simplest). The only problem is that starting positions vary in desirability a lot and one could get rather lucky or unlucky with the Desert Eye map, as the case may be.

Would be interested if anyone know of other wrap-around maps that is challenging to play in SP but with more uniform starting positions.