Except that 'baby' kings are eating pinkies, which are VERY digestible. Fuzzies or hoppers (mice) take longer to digest because they have hair & slightly bigger bones, & I wouldn't want any snake to regurgitate if fed too close together. I'd stick with no meals closer than 5-7 days, & yes, find a more experienced vet.
Also, it's better not to generalize about the size of prey versus the widest part of the snake's body, since it very much depends on what KIND of snake you're talking about. It's fine for many commonly kept snakes, like BPs, but when feeding a snake with a narrow face (for example, a TX longnose snake or a desert glossy snake) this does not apply- their narrow face DOES limit the size prey they can handle.
While many/most snakes "can" eat prey that's a little wider than their body, & in the wild, no doubt they may have to for survival, it's something I avoid doing.
I feed prey that is narrower than a snake's mid-body to avoid problems digesting & also to avoid over-feeding.