Oh it completely sucks. I suspect in my case it's duE to lack of proper tangents.
I know an irregular, assymetrical shield canwork as I used the Vasari minelayer shiel on a Nantes sized model with great effect--except under heavy fire the entire shield becomes visible as a ghostly Vasari minelayer.
I think using layered geodesic shapes, hexagons, polygons, bubbles, triangles or even extruded and connected blobs can work but the effect here surpasses my efforts due tolack of skills on my part.