I said, "Actually they are just as effective as a regular stab. Think of the system with a 10 percent chord elevator. You get a certain pitching moment with elevator deflection and is good enough for a lot of airplanes. As the percentage of chord of the elevator is increased the pitching moment at the same deflection angle is increased until you get the percentage chord to be 100 percent. The pitching moment with percent chord always increases although the increase might not be linear. "

I missed something in there. Why I just remembered it now, I don't know!!

If you look at a regular wing section going up through the stall and post stall you get a given CLalpha curve shape. If you put a flap on the section it creates an incremental CL increase at each angle of attack. There will then be all flying horizontal tail designs with small elevators deflecting in the same direction as the flying tail that make the combination design more effective than just the all flying tail. But these are hard to make and probably not necessary.

The question is then - how does a fixed horizontal tail with respect to the fuselage equipped with a moveable elevator compare to the all flying tail. There will be some airplane angles of attack where the horizontal is at the section Clmax and when the elevator is deflected in the right direction that will have a higher Clmax than an all moving horizontal tail can achieve. But for the majority of the possible tail loads (those that don't approach the Clmax of the section) that either system can achieve there isn't any difference between the two in effectiveness. Indeed at the condition where the elevator approaches 100 percent chord it must approach (probably in a funny nonlinear manner) the all flyling horizontal tail in effectiveness.