Setting the number of civs in a custom map?

[Warman11]

I have made a map using the BMP to WBS Converter. However, the "number of civs" option seems to do nothing. Even though I set exactly six starting plots and selected six civs in the converter, the game still starts with seven civs on the map. I would like there to be exactly six civs, and still allow the player to select from any civ. Is this possible?