Income and population mechanics

[Kobal2]

Originally Posted by Nightfall

Not exactly, a second early fortress and lab is a great start, a third early fortress and lab makes you a big fat target at exactly the time rush builds are looking for one.

Actually, I'd say the more fortresses you have the less you look like a rush target. In the early game, sieges are a pain in the neck.
It's even less of a concern for Man because a) everyone knows their fortresses are going to be even harder to break than average and b) everyone assumes they're gimps in the late game.

Which, y'know, they probably are at that.
But more often than not they do get to see it, because in my experience people try to snuff either easier or more ultimately dangerous targets first.
It doesn't help that Man's early game is actually pretty strong - longbows and knights with magic weapons shut down many different sacred rushes, air magic stops elephant rushes dead in their tracks, a handful of spies quickly make rushes that depend on cap-only units or mages unsustainable.