I think that you really should contact Horseman about the proper arrangement of your ground glass and fresnel lens (the magnifier sheet). The most common arrangement for cameras designed for it that I know of is to have the frensel toward the lens, followed by the ground glass with the ground side toward the lens. You don't want any more glass. You don't want any glass between the lens and the ground surface of the glass.

Contact Horseman and ask them. We can speculate all day on this.