Max,
the system does not automatically compensate for anything, once tuned. The force generators are units containing dual eccentrically rotating masses, which by altering the phase will generate a force in a particular axis and frequency.
The perceived vibration will vary as a function of payload and the relative mass of fuel and load is significant - together they represent a 1/3 of the total max weight, so 50% of the empty weight. Generally, heavily loaded aircraft have greater fuselage damping, so will feel smoother.
I don't believe this argument is relevant to anything relating to the MRGB.