My first instinct when I read your post was that the backs shouldn't be dry if you are getting leaks - I think something is going wrong there.
I second what Natty said about hemp, although I wouldn't personally use microfiber on a heavy wetter if you can avoid it as once it gets very wet it won't keep the wee in - it will sort of squish out if you see what I mean. I would defiantly try and avoid it at night. We only really use MF when everything else is in the wash.
I find the absolute best combo of inserts for daytime pockets is an easy peasy hemp insert, wraped in pettis dessous bamboo insert. Bamboo is still very absorbant, and unlike hemp, it stays nice and soft in hard water. I can't use hemp that isn't going in/under something because it goes to hard and crunchy. Hence why I couldn't use Ellas house nappies or something like that.
I know it is all so confusing to get to grips with, and the hardest thing is that everybody finds that different things work for them. So I would only buy one of something at a time and give it ago.
At night time, the only thing we have found that works without having a massive bum is an upsey daisy night nappy in french soy, it is so slim fitting and soft and absorbant - I love it! At the moment we are using under a ME airflow but when she grows out of them we will get some woolies as these help allow the nappy to breath.
I hope that helps a bit. I wish I had known all this when I first started up with washables - I don't think I would have ever bought a cotton nappy.
Hemp and bamboo is defiantly the way to go if you have a heavy wetter. I am hoping I can use all my (hundreds) microfibre inserts for DD2 when she is born as the newborn won't need as much absorbency.