If you have perfect/acceptable left AF with D800 and 24-70mm, I need your help

I think that your results are probably dominated by the off-axis performance of the lens, which isn't perfect (though I think for a zoom it's quite good.)

It occurs to me that if the best possible focus at a certain point in the frame isn't perfect, perhaps the AF system has more trouble picking the optimum focus regardless of calibration? I wonder if that could explain the lens differences we're seeing with the cases that are not as severe as this thread's OP.