Aircraft stability is determined by the relative location of ac and cg, irrespective of wether tailplane lift is positive or negative.
For equilibrium, cp location with regard to cg is what matters. For an equilibrium condition, total airplane's lift moment about cg must balance any other pitching moments (due to drag an thrust).
Normally drag line of action is below cg, so it creates nose up moment. More often than not, so does thrust (good characeristic in case ong engine failure).
Wing lift acts somewhere behind the 25% chord, depending on the aoa (the less the angle, the further aft the cp is). It normally creates a pitch down moment, but it can be pitch up at high aoa, with an aft cg. Probably this is what they do in those models?
Tailplane lift must balance the net pitching moment of the other forces, plus the pitch down aerodynamic moment of the wing. For normal flight conditions in typical transport airplanes, it is a downwards force which must be balanced by wing lift just as if it was weight.
An aft cg means taht the wing lift nose down created moment will be less, so that the nose up moment required from the tail is less, so that less part of wing lift is wasted in balancing "apparent weight".
the wings will decrease AoA and the tail will increase AoA...
If wing aoa increases, so does tailplane's. Can't be otherwise.