Actually I think it was determined in the sailplane circles.. that having
the CG at the 85% point was the most efficient..
too far aft was too much and caused nose down stick putting the elevator
down into the slip stream, and not far enough aft caused back stick or up
elevator into the slip stream.
Heavier pilots do add tail ballast which increases the minimum pilot weight
for club gliders.

BT


Just to add a bit of noise to the discussion, an airplane operating at
maximum allowed aft CG is actually more aerodynamically efficient.
Sailplane pilots often add tail ballast for just this reason.



--
Vaughn