MANWHORE,
remember that the lens flips the image upside down; like your eyes (your brain then reverses the signal from your retina so that it looks right-way-up).
So, if the cut-off shield is at the top of the assembly, the light is released at the bottom, then switched upside down by the lens and light will come out the top only.
Similarly, if the cut-off shiled is at the bottom, the light is released at the top, switched by the lens, and only light is released at the bottom (correctly.
I think we've put it together the right way