If you take another peak at the link I provided in the earlier post I also compare low ISO DR between the D800 and Df. The reason larger pixels have less dynamic range is because a larger pixel holds a larger charge (more electrons), and the process of holding and reading out those extra electrons creates extra electronic read noise. Also, with more, smaller pixels (higher MP), more of that electronic read noise can be averaged during the process of downsampling to produce the equivalent MP image as the larger-pixel sensor. This is why for example the 12MP Nikon D3s has a relatively poor base ISO DR of just under 12EV vs 14EV+ on the A7r/D800. With the introduction of the D4 sensor, Nikon improved base ISO DR significantly by using what is purported to to be Aptinas (
A-Pix technology, PDF
here), which allows two levels of conversion gain, one optimized for low ISO and the other for High ISO, but even with this significant improvement the D4's low ISO DR performance is still 1EV below the A7r/D800.