Same plane, same CG, 2 different stabs. Plane snaps cleanly with smaller stab, plane does not want to break and snap at all with larger stab. Same wing, same CG, same set up
Just as a start point, when I used to do O/D pattern planes, I used an old formula for calculating the C of G:
CG= MAC/7or6, + (2or 3 x
TAIL AREAx moment arm length)/8x wing area.
This gave a front-to back range(and a comfy c of g was usually 2/3 back along the range,for me anyway).
So,the bigger the tail area,the further back the c.of g.
If you use the same c.of g. for two different tail areas, the larger one will give more stability, and if that (same)c.of g. is far enough forward, the plane won't want to depart, as you said.