Look in your AOE3 directory, in the RM directory and edit the files like this one called texas.xs with notepad. Make sure the readonly attrib is off. The number that shows 30000 was like 10000. I changed to that, and the 3.0*sqrt was 2.0 before I chaged it. Change those and try any size.
// Picks the map size
int playerTiles=30000;
// if (cNumberNonGaiaPlayers >4)
// playerTiles = 9500;int size=3.0*sqrt(cNumberNonGaiaPlayers*playe rTiles);
GOOD LUCK
Fenryial
PS just keep a backup of the file before you mess with it.