Lovely shots! I don’t use any extension tubes, just the lens, I also use 2 constant lights and a speed light.
I’d say increase your Aperture to maybe around 5.8 - 8ish that will make the detail slightly sharper!
Also, the sigma is fully manual, the only settings to change really are the aperture and the focus , you should always keep ISO to 100.
I always keep my aperture around 5.6 to 11 F/Stops and the only setting I change when im shooting is the focus, moving the focus from front to back with each shot to then throw em into my focus stacking software to compile the full focused shot.
If I don’t use the focus then I move whole camera forward tiny steps at a time to focus from front to back to then Stack