Do you typically need to calibrate your lenses on this body? Have you did so on 135L, and have you got good results from it both on full body horizontal, face and far (infinity focusing) @ F2?
I ask this as i do not believe it is possible to properly correct misalignment of mechanical parts in the body (bayonette, mirror, secondary mirror, AF sensor and imager sensor) by simply dialing-in some delta in AF sensor readout.
That's why you have to correct the sigmas with a dock at different distances, as well as to correct every single lens.
What sigma tried to do here is (i guess) they dialed in some kind of correction into their lenses, which is no-no. Maybe they did so to compensate for focusing mechanism ballistics, i don't know. What i know is, if the body is spot-on, there is no need for any kind of corrections for "dumb" lenses. And i have "dumb" body too (Kodak 14NX, nikon guy here). All i had to do is tune it mechanically, since then it is tack sharp, on any distance.
Canon and Nikon both recognise that mfa is often necessary for lenses due to manufacturing tolerances and the higher degree of scrutiny that images receive thanks to high mp bodies. They both recommend in documentation to set the mfa value for a lens at the focal length, focus distance and type of lighting you are most likely to be using the lens in.
It's not just a Sigma thing.
Sigma allows us to go one step further and fine tune a lens for many different focal lengths (four with their zoom lenses) and many different focus distances (four again). This is an improvement on the second rate, coarse adjustment available to us in Canon and Nikon cameras