When you do a reach back, keep your throwing arm high, nearly at shoulder level works well for most people. I think newer players generally throw with the throwing arm reachimg back too low and they will open up when they throw and the throwing arm will end up high and to the right, RHBH on release. As a reesult your disc quickly goes into a hyzer line, goes up high, stalls and dies. Watch the Dan Beto videos and he shows how to keep your arm up high and throw straight. Then it is lots of field practice at that point.