The fact though that we can use only symbol fill with 0% opacity in building material section fill and surface with 100% transmittance, makes this setting limiting. how about a range of these values say opacity up to 15% and trasmittance 85% and more? giving some oportunity for shading between these ranges. And leaving the ranges from 85%to 50% for transmittance and 15% to 50% for opacity to show only the edges of elements behind them.
Even though if shading cannot be achieved which I doubt, these limits have to be set to lower values than 100% and higher than 0% because especialy transmittance affects how the surface will render and how it is seen in 3D window.
The fence material for example with 100% transmittance works fine in 3D Document, renders fine if you set atenuation to maximum but with 100% transmittance it cannot be seen in OpenGL window. I think That this feature was only made for the Air Gap.