Do you mean to say that the ability to sleep is getting further away?
I've experimented to some extent with combining kava and a substantial dose of passionflower, which some claim has a doubling affect. Passionflower by itself does nothing for me. It's also probably typically OK to combine kava and chamomile. I've tried combining kava with ashwagandha, though the science on that combo is questionable, ashwagandha does seem to have a slightly more noticeable affect than other herbs. I've also heard of combing kava with holy basil, but holy basil is an herb that reduces cortisol (like rooiboss), which is something to be aware of when combining with other medicines. Some claim holy basil is very sedating -- for me not so much. I've also tried teas with skullkap and catnip or lemonbalm, but they never do anything for me.
I'm not qualified to speak on valerian, but I have tried it; it seems to lower my body temperature and makes me feel cold, but wasn't very sedating personally. Some say you have to take valerian for over a month before it starts to help with sleep, but that's another topic all together.
Personally the only combo I've notice really working is kava + chamomile or maybe ashwagandha.
EDIT: for doses of kava, 4-6 tbs of medium ground for cup or cup and 1/2 is a heavy dose; 2-3 tbs of micro is substantial. As for strain, it's different for everybody: personally borongoru is very sedating to me, but others say boroguru is more sedating.