A cylinder, piston, rings and everything else change shape when they heat up.
A cylinder might be perfectly round when cold but slightly oval when hot. A ring that was broken in on a cold, round cylinder will not seal that cylinder once the engine reaches normal operating temperature. That ring has to be worn to an oval shape too..
So, get the engine hot by idling for a long time so the shape of all the parts is stablized before beginning any breaking-in schedule.
And there are other mechanical forces at work that change with different riding conditions.
In essence, the way you break-in determines under what conditions the rings will provide the best seal.. If you break-in at low engine loads and low speed and mild engine component temperatures, the rings will seal very well at low loads, low speeds and mild temps..
At high temps, speeds and engine load the sealing ability of those same rings is pretty much unpredictable.