Before you can understand the effectiveness of the horizontal stabilizer you need to know exactly what the stabilizer does. To put it simply, the horizontal stabilizer provides a down force to the back of the airplane to keep the nose up. This is why stalling the even just the horizontal stabilizer will put the airplane in an uncontrollable dive. The further aft you put the CG the more effective the stabilizer. The further forward the less effective. This is why a severely tail heavy aircraft will pitch up no matter how much down elevator you add. In that case, you must throttle down to reduce the flow of air over the surface, thereby reducing its effectiveness. That's also why a very nose heavy aircraft needs to gain a lot of airspeed before the pilot is able to rotate off the runway.