Aperture is set in 1/3-stop 'steps' (default, can be changed in C.Fns) regardless of ISO. Of course, at the expanded ISOs (50, 102400, 204800) are full-stop increments below/above the native range, so in an auto aperture mode (P, Tv), setting ISOs in the expanded range means full-stop aperture changes instead of 1/3-stop.
Not sure if that's what you mean. Can you explain a bit more what you mean?
