Natural Wonders: A major civ's starting location isn't allowed to be within 4 tiles of a natural wonder.
But a city state just isn't allowed to be adjoining one; and can be two tiles away.
City states one tile away from a good location: City states always found in place; the AI might be willing to shift one tile if they can still found the same turn.
Also major civs starting locations are before all city states.
City states appear to have a coastal bias.