Part of it also seems to be how long an empire holds ground in the rankings. The Guardians have more points, but not the longevity. GROSS also held an unusually large percentage of the map even after falling out of #1 and down into the lower part of the top 10 for a long time, and it was clear the Fellowship at that point in time was a superpower still with more battles, so I was suspicious there was some kind of lingering effect linked to how long an empire had been at that spot.
So we have points, battles, and longevity all in the equation. How those parts interact exactly and if there are any more factors thrown in is a mystery. Unless T-Man or whoever programmed the map code wants to let us in on the secret, then I would guess students of the Meta are going to ponder a bit longer over the riddle of the map unless one of us solves it. Now you see why I advise my own ship mates to ignore maps. There is just one direction, forward! And that goes for both empires and overlords alike. So don't worry about the map, just keep moving on up game by game.