AI Human Mega Evil Empire Score Percent:= 170

[Daynarr]

It means that if human empire (that has the highest score of all other empires - AI or human) reaches a score that is 70% larger then the 2nd player (AI or human), that condition becomes true. Also, the other condition in setings.txt is also important - "AI Mega Evil Empire Threshold Score Thousands" (minimal score necessary for empire to become MEE, it prevents players to become MEE too early in the game). If the empire has both conditions true, that empire becomes MEE.
Of course the AI has higher percentage threshold because it isn't as smart as human player and will not be able to utilize its advantage like human would.
In short, it determines which empire will become MEE, not the score you will get if there is MEE in the game.