It's all a big conspiracy by NLS to starve your fish and steal your money...
Thanks for the chuckle, Matt.
Over the past decade I have probably fed NLS to more species, and more individual fish, than anyone on this forum & I can assure everyone that there are no exact hard & fast rules as to what size of fish will readily consume what size of pellet. Some general guidelines such as what Water posted, but some fish will handle the larger pellets at much smaller sizes than stated earlier. As others have mentioned already, if your fish are chewing too much it will be one of two things, too large of a pellet size, or the fish are simply adjusting to a harder more dense pellet than what they are used to.
As far as pellet size, with most of the larger CA/SA species, I start the 3mm pellets at around the 6" mark. By that time the fish are well accustomed to how dinner plays out in the fishroom, and there's no muss, no fuss, and no chewing. I currently have a 7-8" red devil mutt that will hammer back multiple 3mm pellets at a time, and in the blink of an eye he will easily crush them with his pharyngeal jaws - then straight down the hatch. No waste whatsoever. It really all boils down to how aggressive an eater each individual fish is, but still, the pellets should always be comfortably matched to the mouth size of each fish.
BTW - with the exception of a Mbu puffer, and some Asian aros, I have yet to come across a fish that I couldn't train to eat NLS. Some take to it straight out of the gate, others take a bit of time, but you'd be amazed how fast a fish will learn to eat food when no other options are offered.
edited to add - Jeff, maybe you could post the pic of that juvie & the 4.5 mm NLS pellet. lol