It's an old tourney game, AFAIK the corruption settings haven't been altered. I did a bit (ok a lot, this is driving me crazy
)more testing after your post though, and my capital always had 1 shield and commerce wasted after it reached a good size, no matter what the number of cities, so you can't use the method you suggest very easily. The result of all the extra testing was that I still can't find any effect on waste or commerce of number of cities. If people can look at any old saves games where they have the number of cities relevant to the supposed corruption threshold for the map that would be useful.