The Shadow "knows"

[LavCat]

Both Master and Warrior use your base armor for torso and headgear (you should consider donning high-end elite armor for torso, perhaps with Hels socketed, before summoning, and similarly the highest you qualify for of: circlet, coronet, tiara, diadem, since those will skyrocket the potential affixes the shadow rolls for headgear, afaik).

Thank you, Crystalion, for the research! Can I conclude from this that for casting, putting on a plus three shadow great helm of restoration, rather than a plus two assassin skill rare diadem is probably a mistake?

In the first case the shadow master level is 28 and in the second it is 29.