Question about AI difficulty scaling

I'm a scrub who only plays against the AI. I play on DE now.

How does difficulty scale? I can pretty comfortably beat a moderate AI on Arabia. What would the next rung up be? A 1v1 with hard AI? Or two standard AIs?

I guess what I'm trying to ask is, how does having two or three opponents compare to having one harder opponent? Would it be harder to beat one extreme AI, or three hard AIs? That sort of thing.

Maybe there's no clear answer. But I was just curious and figured I'd ask here.

Thanks.