I am using the classic Wollaston design. The meniscus lens is placed behind the aperture stop cards, with the concave face of the lens facing the subject. The location of slot for the stops is 10~15% of the focal length in front of the lens.

Here's how Wiki shows it...
http://en.wikipedia.org/wiki/Camera_..._camera_lenses

The lens barrel is quite deep, so there's a very effictive lens hood inherent in the design.

Reinhold