A few notes.
Lycoming's IO-390 operating manual is clear: Oil Temperature: The maximum permissible oil temperature is 235F. For maximum engine life, desired oil temperature is 180F.
Something over 200F during a slow climb is to be expected. Look at the oil cooler performance charts, and note how airflow affects cooling capacity. Pressure drives the flow. At 120 knots, available pressure is only half of that available at 170 knots.
It's often stated that an oil temperature of 212 or higher is desirable "to boil the water out of the oil". Actually, water evaporates just fine at room temperature; temperature increase just speeds the process. At 180F, the vapor pressure of water is about 30 times the pressure at 59F.
Boiling merely demonstrates that vapor pressure has exceeded local pressure at some location in the liquid. Local pressure drops with altitude, so boiling temperature at sea level isn't relevant anyway. At typical RV cruise altitudes (8500~11500) the boiling point of water is in the low 190's...not that it matters.
Higher overall CHT and oil temperature during break-in is to be expected. However, I suspect some seal and baffle work is in order. It seems to be part of the Phase 1 process for most builders. Here the forward governor doesn't help.
My oil temp sender indicates about 7F warmer than actual. If you look up the specs, the tolerance for those senders is really wide. Give yours a reality check.