Sony A7r III with Canon 1.2 lenses - Aperture error - 1.3

Have been using my Metabones Adaptor with the a7R III for Canon EF glasses.
However, I notice that with both the 50/1.2L and 85/1.2L II, both lenses only open up to f1.3, and not f1.2.
I am curious as to why that may be? Is it Metabones problem? Canon's? It obviously does not matter to the images, but I am curious why that may be the case. Anyone?


The lens is fully open but aperture is 1.3 not 1.2.... Anybody has the same problem?

Aperture=lens focal length divided by the diameter of the entrance pupil.
Does the entrance pupil diminish slightly when mounted on the adapter or is the travel of the aperture lever diminished?
Entrance pupil is the diameter of the aperture opening when viewed through the front of the lens.