StarFire - agreed, but you have to start somewhere. If the idea is to minimize as much as possible the interactions then the full symmetry is the way to go. If the idea is to get an airplane that has the same interactions upright as inverted then full symmetry is still good. At least rudder causing pitch coupling due to the sideslip/downwash mixing is going to be the same whether the belly or canopy is up. As a matter of fact the only factor that is left that won't at least be consistent in coupling effects is gravity.

ilikeplanes - you want the fuselage longitudinal areas, mass, thrust and all of the stuff to be all lined up. The idea is to give the forces no moment arm to couple about the CG. You have to have the wing lift and the tail lift there with moments to stabilize the airplane but in a case like the Citabria the wing is quite a bit above the CG and is positioned above the tail, rudder and fuselage. It does make for a lot of coupling.

The Citabria has a negative Clbeta term due to the high wing. This means for a left rudder input you get a positive sideslip (nose left) and the rolling moment the Clbeta term produced is negative (left wing down). The anhedral in the wing lowers the magnitude of the Clbeta term. Lowering the wing does the same thing. Distribution of area about the CG can effect this also but to a lesser extent.

Basically you can adjust wing position and dihedral to give a zero Clbeta term for a small range of angle of attacks and sideslip angles but then with high angle of attacks or sideslip angles you get variations in Clbeta also.

It is a big balancing act in which you try to minimize the inputs.