A lot of times it is simply not being level when you think you are. At altitude the perception is different and many times guys simply are either inside or outside wing low. If it is consistently dropping the same wing, as you come in to the spin, slightly correct in the opposite direction you think it is going to go and see if that helps. That will tell you if you are truly level or not. Also, on some planes, the plane will break very abruptly. Usually has to do with wing shape and such. One such trick to this is to carry a little power as you come in to the spin with the nose up. As you get to center, you can just chop the power and it will let the nose drop.

I would definitely try the test to see if you are actually level first though. That is usually the issue.

Arch