The analogy with the see-saw was probably imperfect. I shouldn't have posted it. This explanation by Genghis is certainly much better:
Originally Posted by
Genghis the Engineer
CG is quite close to, but in front of, the centre of lift. Moving CG aft moves it closer to the centre of lift, so that the tailplane has to do less work to match the pitching moment effects of CG and CofL not being in the same place.
So, it becomes more effective, since any elevator movement will be more powerful in terms of pitch response.