I would think that you would want to project onto the textured side. You can certainly call Carl's and see what they say.

The concept is that the textured side is the diffusion layer. So, you will get better light diffusion from that side and light will more easily pass through the smooth side. You do NOT want the light to pass through (and reflect off of) the smooth side, then hit the diffused side (creating more reflections), then back through the smooth side. This ends up creating three points for light to scatter and cause reflections and not look as good.

Given enough distance, you won't have a major issue projecting onto either side really. It just won't look quite as good, I expect, projecting onto the smooth side.