Both. Let me show you 2 screen grabs of some results. The first is my 24-70. I took at 26mm by accident and at 70mm. You have helped me by explaining the differences that can be seen between the two focal lengths, which you must admit are extreme.
I will e-mail Michael Tapes and ask his opinion, but up to now I've been using the distance tool on his website for the two focal lengths i.e 2.1ft and 7.1ft.
Interestingly I did a test on my D7000 with the Sigma 50-500mm OS and the results were heartening especially at 35ft as per the distance calculator. See last screen grab.