Completely agree with rmh.

If the elevator has anything but neutral trim for horizontal flight, how can it act as a neutrally trimmed rudder when the roles get switched during knife edge flight.

CG location and wing AOA are key factors in the degree of trim that the elevator requires for horizontal flight.

Can those be adjusted to allow a perfect hands and trim free KE?, probably yes.

Would those adjustments generate undesired reactions for non-KE flight?, probably yes.

Experimentation is the key here