I think the answer is pretty clear.
NRT/HKG flights booked through United as part of a larger itinerary will earn 100%. This is consistent with UAFlyer and Yoosh
Flights booked through United on NH metal that are not NRT/HKG receive the 70% per Taipei's case.
The only question is if you purchase NRT/HKG RT and not as part of a segment of a United itinerary will it also equal 100%?