I think it might just be worth clarifying the logic here, to make it totally clear that an orography field does not interpret this at all
i.e. you can regroup like this ..
```
    if v_type not in [field.int_mdi, NIMROD_DEFAULT]:
        if FIELD_CODES.get(field.field_code, None) == "orography":
            orography_vertical_coord(cube, field)
        else:
            vertical_code_name = VERTICAL_CODES.get(v_type, None)
            if vertical_code_name == "height":
                height_vertical_coord(cube, field)
            elif vertical_code_name == "altitude":
                altitude_vertical_coord(cube, field)
            elif vertical_code_name == "levels_below_ground":
                levels_below_ground_vertical_coord(cube, field)
            else:
                warnings.warn("Vertical coord {!r} not yet handled"
                              "".format(v_type), TranslationWarning)
```