Richard,
Full throttle. Bushing type bearings, such as the connecting rod, should be broken-in fast. At full throttle, running a bit rich and with a smaller than normal prop, the bushings build up good film pressure with the oil on the bearing surfaces.
Full throttle also allows the cylinder to get up to operating temp and expand the needed amount.
The smoothing and rubbing of parts is greatest during the first few minutes. That is why an ABC engine runs much better after a few runs. The wear-in procedure will continue for about an hour to a lesser extent and you may notice the engine running better and better during this time.
I think the amount of improvement you see during the first hour, after the initial runs, is partly determined by how well you did those initial runs.
This is personal opinion, there is rarely only one way of doing things.
George