What is an unsatisfactory needle split? and its ok the next time?
I like to see a decent drop on the engine vs. rotor rpm, 15-20%, but a hot machine will often take quite a forceful drop of engine revs to achieve it, which is of itself not always good for the engine.
Sometimes it works best to roll the engine revs up from about 50% to 75% then immediately cut the throttle back, as the rotors are gaining momentum and it seems easier to split.
I'd say a minimum 5% split would be my go-decision. If I couldn't achieve that, I'd want to know why.