I think whoever originally said that contrast was "controlled" with the lens meant that it was affected by the characteristics of the lens, not that there are ways to change it by adjusting the lens. Hence my "replace it with a different one", which may have sounded like I meant something was wrong with the Busch lens---but if I wanted to change the contrast of the resulting negative, and I was limited to using the lens to do that, I'd do it by going and getting a lens with different contrast.

(Though I guess the couple of posts above, pointing out that flare affects contrast and so shades and aperture choice have effects, are right too.)