Internal micro lens focusing has always worked better for shooting jewelry for me but other caveats arise.
1.Camera movement from the structure my camera stand is on.
2. Strobe LIGHT has a different refraction SOMETIMES DEPENDING ON THE DEPTH OF FOCUS. (causing blurs)
3. Camera sensor sometimes records different color file.
4. There is a limit and time factor that I can tolerate shooting one piece.
5. Focusing around and DOWN a corner the increments set in a standard pattern can deviate in a big jumps in the depth. meaning you might need only 1 increment what ever that is or you might need 5 smaller increments.
6. The shape of the object can really effect how you shoot so every stacked image is different depending on the shapes, height, width and depth.
Moral of the story if its important shoot more that one stack of the same object and learn to love ALMOST PERFECT!!!
Nice write up.