LOL. I bet this is a misconception because the lens is actually at f2.8 before the shot is taken, not wide open at 1.2. Thus when you disconnect it in the above example, the 85 1.2 is actually at f2.8 not 1.2.
This confused me with my sig 85 1.4 initially, especially when using LV and DOF preview - I'd set the aperture at 1.4, press DOF prevew and the image would change. Then I looked at the diaphragm before taking the shot and realized that it was set at f2.8, not wide open at f1.4. Of course lenses with max apertures of 2.8 or greater will be at their maximum aperture before the shot is taken.