ORIGINAL: WWIIbirds
I assume the effect of downwash to be negligible due to my offset wings so I'm not including it my calculation. My concern is that to calculate neutral point it's all about calculating moments, with in line wings I have 2 moments created by the lift of both wings but with offset wings not only do I have lifting moments but I also have moments that are created by the drag of each wing.
I believe that your reasoning is correct.
Please read this old thread:
http://www.rcuniverse.com/forum/m_10456424/tm.htm
Consider however, that for flight stability purposes, the Z axis is irrelevant and the stagger of the wings will move the CG along that axis as well.
We want the center of lift and drag to be aft the CG in line with the airstream, which is what created the aerodynamic forces that stabilize the plane in pitch and yaw.
The drag introduced by the wings is also directly proportional to the lift produced by each wing at each different speed: it is a dynamic force.
If your canard is much lower than the main wing, for example, a nose down pitch will be generated by drag; however, that moment is to be compensated by trim (because is dynamic or dependent on speed) rather than by manipulation of the CG.