I'm glad that you brought up the topic because I have had my own theories about how kava effects sleep.
Kava interferes with my sleep in the same way drinking alcohol or smoking cannabis would. If I go to bed krunk then I'm yawning a lot the next day, even being in bed 8-9 hrs. The yawning is from a lack of deep sleep. Or from waking up in a half-sleep state whether I remember doing so or not. IMO it can even make you wake up more easily from sounds or lights, since kava makes you sensitive to those.
Like alcohol it can help me pass out, but quality of sleep is different. I can be the guinea pig here since I have had insomnia problems for a while now. If I drink 4-6 tbsp (not right before bed) then my sleep is usually fine, any more then the effects are obvious. I can also tell because when I don't drink kava I may wake up a few times during the night, but I still feel more refreshed the next day.
2 or 5 chemotypes might help with passing out but they can also increase fatigue the next day, which is the catch 22 for anyone taking a med or supplement for sleep. The more you take the better you could sleep, but the more the hangover, and sometimes you don't sleep either way so you're tired *and* hungover.
If I were to rate NOBLE kava (tudei is horrible) as a sleep aid I would give it 3/5 stars. It helps indirectly by reducing anxiety, which is great, so therefore sleep should be better. I have taken awful meds which make you a zombie the next day: kava doesn't do that as much, and there are less side effects. However if someone has true insomnia kava is sort of a bandaid. For any normal person trying to sleep it should definitely be enough, and better than getting prescription drugs. The shit the doctors give you is unbelievable sometimes -- antidepressants with 20 hour half-lifes which make you incapable of driving a car for 3 days.
The only thing that really works for me is quetiapine/Seroquel. It has a short half-life and doesn't make me retarded, even though there are side effects. I drink kava in the evening and take that at night.