I'm a bit confused, I would assume that pound for pound, and any airplane where you simply move the wing and change from a tail downforce to a canard you would gain additional CG range. The assumption going that for the same weight in payload the wing would have to produce less lift than before since instead of compensating for tail down force, there is a net gain in lift due to the canard.
Example, 2100 lb aircraft, requires 200lbs tail down force, so wing produces 2300lbs of lift for level flight. If changed to a canard, and the canard produces 200lbs up force, total lift produced by the wing would be 1900lbs, hence less weight. Less weight equates to a lower moment allowing for a greater arm of cg before max tail up force is reached, giving a net gain in CG range.
Am I missing something basic here? Are we simply talking about a normal aircraft that has had a canard added in the front to create a smaller elevator/stabilator?