New Sigma 35mm 1.4 bokeh

During my initial experience with the sigma 35 in comparing focus capabilities to my nikon 24-70 in low ambient light, I too noted some tendency toward underexposure in the sigma with both set at f/2.8 and the 24-70 at 35mm. I found about one stop difference. I subsequently noted that the vignette control and ADL had been turned on in that shooting menu and wondered if recognition of those settings on the D4 was different between the lenses. The sigma also seems to demonstrate slightly less magnification (is sigma a short 35 or nikon a long 35?)