Stencil Shadow Volumes - End capping

I have finally found the time to have a go at shadow volumes and based my development on the “Practical & Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering” by Cass Everitt & Mark Kilgard. (Great doco btw)

My question is this, has anyone else found that they need to use the back faces at the end caps at both ends of the shadow volume?

If I’ve read the doco correctly (and I’ve stared at it for the last 3 hours or so…) you cap the volume with the front faces (drawn normally) and the back faces (extruded to inf.).

But when I do this I get a shadow on the near side of the object (relative to the light).

To fix it I draw the back faces (in their normal positions - only with the vertices reverse - ie. instead of p1, p2, p3 I draw them as P3, P2, P1) as one end cap and the other end cap is the back faces extruded to inf.

What I’ve found is that I don’t appear to get a shadow on the rear faces of the object (which I kind of expected) but overall the shadow appears OK.