Shadow Form Transparency vs. Opacity (Patreon)

Obtenebration has a "Tenebrous Form" power that allows a vampire to transform themselves into a pure shadow that can only be harmed by fire, sunlight or magic.  There is also a power called "Shadow Twin" that animates a vampire's shadow into a weaker duplicate of themselves. Obtenebration users can also use a power called "Night Shades" to "Summon shades to act as Servants".   We are experimenting with lighting and alpha transparency effects on portraits of characters in Princes of Darkness mod. For us to show one of these shadowy avatars, how much transparency should the shadow avatar have?