Ok, well
Im not a good teacher by any means but I'll give it a shot. Ok first off, you should try to lay your middle finger upon the stick. It feels really akward at first, but try putting less choke on it, and it will get easier. You just have to find a good place to posistion your hand.
Then you said your fingers keep coming off of the stick.
Im guessing you mean maybe middle, ring and pinky. Well, you just have to practice keeping your middle finger on it, and not applying any pressure to your middle finger. And as for your other two, don't try any bounces or anything. Practice playing single stuff just anything as long as its anything but diddles and rolls. Then when you get used to keeping your all of your fingers on the stick, just try to keep your pinky and ring stuck together and they shouldn't come off of the stick. And keeping your middle finger past your ring and pinky helps keep your pinky and ring intact to the stick. Just always keep your hand very relaxed, but think of it as your pinky and ring are glued toghether at the tips, but they stay very relaxed. Just stay relaxed, but some pressure in your thumb, stroke, and just let your pinky, ring, and middle go limp pretty much.
As for stick heighth. Well the only thing that ever caused me to not get good stick heighth was that I played very choked. And just recently have I put my left hand farthher back on the stick. It really helps if you don't choke. It helps two things, keeping your middle finger on, and stick hiegth.
Ok I don't know if those were your problems or not, but I gave it a shot, so if you have any questions please ask, because I just recently fixed my grip a lot and I want to try to help people that had problems like me. So I hope this helped some.