Flying a tail heavy plane is a bad idea! RC planes work like a fulcrum, a little weight in the tail equals a lot of weight in terms of CG (Center of Gravity) and balance. So the further back the weight is from the CG the more leverage it will create and the more unbalanced your RC plane will be.
In this episode of Flite Test, we put a bunch of weight on the tail of the plane to show the extreme effects of a tail heavy plane.