If you are talking about the black polygon glitch, You need a vertex at the center of the shadow. Btw, the inner ring of vertex is probably not needed as you only want to control the shape/contour of the shadow unless.
Correction: ok I think the inner ring of vertex is for controlling the fade out distance. That would be ok but imo, its not really necessary as players generally don't put too much attention on the shadows. 90% of their focus will be on the character.