When I feed my fish, I use a mixture of large, medium, and small pellets. That way, everyone from the 18" koi down to the goldfish babies will have something to eat.
But it seems like the fish all try to grab the LARGEST piece of food, and then either keep pecking at something that won't fit into their mouth, or they stuff it in there and swim around with it, unable to swallow it. I've seen them sniff and then pass up smaller pieces, just to chase a huge pellet they can't swallow.
They would have fuller tummies if they went after food that was the right size for their mouth!