420ace, I've flown the Ki-84 a bit in the AvA matchup against the La-7, and against good pilots I found it absolutely necessary to keep the nose-up so the flaps would not auto-retract. Once you get into a good position you can get more aggressive and follow nose low with some throttle work, but if the fight is equal you cannot go nose low. I've tried cutting the throttle and using rudder, but the flaps still auto-retract in a low yo-yo, which makes the maneuver an absolute waste of the 84's abilities.
Btw, I've been flying the 84 a lot recently, and once you get used to its quirks and avoid its nasty traits, it is a killer. Flying it for base defense last night it seemed like I was landing 5-6 kills every 15 minutes.