I am testing it now, it's been a while since I used the Hyperion for 1s but I don't recall it ever having issues with not hitting 4.20 volts on the nose. Are you guys setting it for solo mode or quick mode?

I've just tested this, for using balance mode you need to modify one of your 2s balance leads. The red wire on the balance connector will not be used. Solder the Blue lead from the balance connector to the positive plug on the battery, the black lead remains on the negative battery post. I am currently charging a battery with this setup and the balance voltage for 1s registers, I'm also charging a battery with no balance lead and will report the results.