On the primacy of exposure

Buzzzzz! It's really hard to determine front to back sharpness with all the changes in tonality, microcontrast and especially sharpness (not just DOF) at different apertures. Too many variables...

What about the groupings, I could easily have swapped D and B and A and F?

By looking at the grass just in front of the gate, this is highest to lowest sharpness imo (with huge license for the last three, as downsizing takes away valuable detail clues):

E, A, F, C, D, B

Since you focused on the gate, assuming a 50mm prime it should be sharpest around f/4-6, so one would guess 13.3, 14, 14 for E, A and F respectively. Comparing this to the list above compiled looking at far detail (which I confirm with perhaps the inversion of B and D, B being sharper) I would suggest:

EV...... F/.... Image
15.6... 11.1.. B
15 ......9.1 ...D
14 ......6.4 ...F
14 ......6.4 ...A
13.3 ...5.0... E
10.5 ...1.9 ...C

But I am not happy with it

jh