The Logitech drivers have a certain non-linearity built into them, which means the forces around the center of the wheel are artificially reduced to prevent oscillation. If you set the force in the drivers to something > 100%, this non-linearity is removed or at least reduced, making finer details stand out more, respectively making the forces more like LFS actually tells the wheel. However, don't overdo it with the force slider, as the curve will start getting non-linear again if you set it too high, but instead in the opposite direction, exaggerating small forces at the center of the wheel.
Another thing to keep in mind is, that CP: 80%, LFS: 100% is not the same as CP: 100%, LFS: 80%. The former will produce much softer and dampened forces than the latter, which is probably also related to the linearity.