Laser Cut Panel (LCP) Modelling Problem

I have run into some trouble using the file that models a Laser Cut

The problem I'm seeing is that when I replace my regular window with one
made of the lcp_material direct sunlight seems to eliminated entirely (both
deflected and undeflected) from the interior of my room. My facade is south
facing and is fully glazed with either glass in the 1st case or lcp_material
in the second. The 1st case, with no LCP, shows a diagonal stripe of direct
sun hitting the wall. In the second picture with the lcp_material, instead
of the direct beam being split into deflected and undeflected portions as
expected, the direct beam is completely eliminated.

I have read Phillip Greenup's paper "RADIANCE algorithm to simulate
laser-cut panel light-redirecting elements". I get the feeling that there's
something wrong with my alignments somewhere, but I haven't been able to
find a combination of -rz material rotation, surface normal of the polygon,
and rotation of the room as a whole that produce the correct results.
Everything I've tried results in the same thing: direct beam sunlight
eliminated from the room. One thing I'm not clear on: the -rz rotation in
the prism2 material definition should point the surface normal of the
material in the same direction as the final orientation of the polygon, and
both of those normals should point toward the exterior, correct? I am
defining the room with the +Y wall being the window and then rotating that
room 180 degrees so that it is south facing. As a result, my -rz rotation is
270, to point the normal in -Y. Unfortunately, the results have the same
problem I described whether the -rz rotation is 90, 180, 270, or 0. I've
included some of the relevant code at the bottom of this email.

I'm hoping this is something that someone else has run into before. I've
been using Radiance for about 8 months, so I've learned some, but definitely
not all, of the ins and outs of the program.

Thanks very much for your help,
Kevin Thuot

#lcp_material definition
void prism2 lcp_material
11 f1 dx1 dy1 dz1 f2 dx2 dy2 dz2 -rz 270
2 .5 1.5

#part of conf2.rad file:
lcp_material polygon window
    16 9 2.8
    16 9 0
    0 9 0
    0 9 2.8

#rotating the room so that the window faces south instead of north
!xform -n conf2 -t -8 -4.5 0 -rz 180 conf2.rad