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When you break in the full size engines you don't lean out the engine right away until it goes too lean.
With full size engines the jetting is fixed and rich unless you change it so in effect they are running 'slobbery rich'. Or plenty rich anyway.
The key here is to limit the temperature of the ring. The ring is a little rough and so is the cylinder causing considerable friction heat. A rich mixture and extra lube in the fuel cool the ring (and other parts) allowing the parts to slowly mate. This and thermal cycling of the parts (thermal cycling changes the parts kinda like heat treating) break in a motor for best performance.