There's no denying that the walls of the Fuchi grid are tallest where they meet the Matrix, but it's also a fact that Fuchi mainframes maintain defenses in depth. It's just as easy to get burned by Red-12 security somewhere on the inside as at the outer walls. And getting out alive is no less a feat than getting in. The rare few who've managed it, in so far as Gordon is aware, all had help from the inside.