A full size jet would have a very good reason to put the pivot point more rearward... namely the shift in aerodynamic center at supersonic speeds. This would place the pivot point at 40 to 45% MAC for supersonic speeds.

I'm not intimately familiar with the SU27, so I don't know where the pivot point is on the full size aircraft.

Realize that for an all-moving stab, if you place your pivot point away from the 1/4 MAC, the AC of the stab will be moving around when you move the stab.... which may or may not make for some interesting control responses. If nothing else, it will put more stress on whatever torque tube you have the tail pivoting on.

Mike... I'm not sure what to make of the photos you posted, Can't quite see where the horiz stab is pivoting.