On a custom map, why cant I change the number of competitors?

Running a huge map, I want less people on it, so I can learn the game.

It looks like when you play a custom map the number of players is locked to the max on the map, I havent figured out how to fix that, but you can edit the number of players on the map itself by deleting the start points.
to delete a start point, right click and drag your mouse over the start point, delete all the start points from that game "mode" and it will go grey instead of red., delete them until you have the proper amount of start points you want.