For the "light metal" I fly, the forward limit for CoG is determined as much as anything, by the effectiveness of the elevator when in ground effect. Ground effect by reducing the authority of the elevator, necessitates up to 15 deg of extra elevator to allow the aircraft to flare for landing.
The flare is simply bringing the wing to its critical AoA and allowing it to stall. As this mathematically links to Lift (by that long equation with Coefficient of Lift, density and velocity) it must also relate to Weight.
For a better description see Kerschner's Advanced Pilots Manual.
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