It all depends on the snake. I have a yearling corn who's still the size of a hatchling and takes large pinks small fuzzies (only fed maintenance diet with breeder). One the other side, I have a 10 month old corn who takes hoppers. Growth rates (the small one is a REALLY slow grower) also play a part.

Based on girth, the prey should be about half again the diameter of the snake's middle. Based on your comparison, I would suggest at least moving up to fuzzies.