AMFA is completely dependent on the specific lens and body combination. I've had lenses require very different adjustments on three different bodies, and there's no consistent pattern of offset - it really is on a case to case basis.
As you suggest, at and near the MFD, the optimal AFMA value can be different (but not necessarily - my 100L on my 1D X is best at +2 at 5 meters, +4 at 2.5 meters, and +3 at the MFD). But...you should determine the adjustment at the subject distance(s) you commonly use, and if you shoot at multiple distances, it's good to test at multiple distances. Personally, I test all my lenses at 25x and 50x the focal length, and weight the adjustment based on my common shooting distances, as well as the DoF effects (meaning more weight usually goes to the 25x distance).