Are they flying the planes we fly? Until they fly a second hand plane that was tuned already, they likely have no idea what they're missing. You can't expect the same level flight line with a trainer wing or shoulder wing plane especially if it's not fully symmetrical.
How about cutting a pipe? Isn't "peak for an OS" is like finding peak on a Prius or Nissan Cube?

Think back and remember, he's running on the rich side to be safe. He's learning how to adjust mixture between low speed and high speed needles. His ARF engine mount is assembled from the factory and that is going to be the thrust line for that plane until it crashes. He's not changing his thrust line for many planes to come. He needs a baseline setup, to pick a prop that didn't come with the ARF, so he saw two brands and wants to pick one.
He's working on his landing, touch and go's, maybe building confidence to fly on a windy day.
His training jargon doesn't include knife edges, coupling, 125% endpoints, or tossing OS for real engines like NovaRossi or Jett who haven't given up, yet. Hopefully everything won't be EP and lipo velcro'd into styrofoam and beer coolers.