I would hope that the calibration was in the Hexar Body. Otherwise the lens would not be "standard" and would be a throwback to the early Leica where the film-to-flange distance was not standardized! More likely F1.2 is a challenge to the cameras calibration, especially at 0.6x finder on the Hexar. I bought a Canon 50mm F0.95, put it on my Canon 7, and the focus was exact. At F0.95 there is not much room for error, like at F1.2. It does mean that the film-to-flange distance must be exact, this is done with a shim under the lens mount of the Canon 7 body AND the RF calibration must be right on. I have built up the RF coupling of a few OLD (~50years) 135 F3.5 lenses, but this was due to age. A new lens should not require this. The Canon F1.4 and F1.2 lenses also have a brass shim that sets distance from the lens module to the back of the lens mount. This piece is picked at build time, and must be precise. They would not have picked this part to make up for some error in the body, and Canon 50mm F1.2 lenses can be used on any standard Leica Thread Mount camera.