If the plane is more tail heavy, it will require more elevator during knife edge.

This is explained with the fact that you carry down trim for level flight and while in knife edge the down trim adds up to the fact that caps push to the belly due to their shape and things I other don't understand...

So I would actualy advise you to try moving your CG forward bit by bit.

Caps have a lot of character and it is magnified when they are a bit too heavy...