The DOF beyond the subject is always greater than the DOF in front of the subject. This means that the distribution won't be even so you need to focus closer than the center of the depth you want.
If you still use a D800, stay away from very small apertures as most lenses will run into diffraction problems somewhere between f/8 and f/11 with this sensor and reasonable reproduction ratios. The D800E, D810 and D850 all have a different Nyquist frequency band as a system because of the weak or non-existent low-pass filter and can usually be closed down to f/13 without too much degradation in quality. The 20-24 MP FX bodies can also be used around f/13 because of their lower sensor resolution.
Trying to understand DOF and diffraction on a deeper than the practical level always leads into quite esoteric physics...