Is there a rule/theory about the relationship between the tail moment and the tolerance of moving the CG aft?

I have found, if the tail moment is short, it is less tolerant of a change in CG back. . . . Hard to explain.. . . In a model I have with a tail moment of ~1.3, flies great with a CG of 25%( 28% is unflyable ). A model with a tail moment of 2.5, flies great with a CG of 33%. I like them at neutral stability.

The longer the moment, the less critical a CG change will have?