I used to make 4x5 duplicate transparencies, as well as B&W and colour internegatives, from 10x10, 8x10 and 5x7 originals. The trick was to use a normal focal length lens for the format of the original, mounted on an enlarger with an extra long bellows draw. In my case, it was a 360mm enlarging lens, on a Durst Laborator enlarger. A shorter lens will work, but you may have an uncomfortably short distance between the lens and the unexposed paper.
If you have a method for reversing the lens when the magnification is 1.0 or less, by all means do so. Normally, the short conjugate of the lens, usually the "back" of the lens, will be oriented so it faces the original, when an enlargement is being made. When a reduction is being made, it should be oriented so it face the unexposed material.
If you have a method for reversing the lens when the magnification is 1.0 or less, by all means do so. Normally, the short conjugate of the lens, usually the "back" of the lens, will be oriented so it faces the original, when an enlargement is being made. When a reduction is being made, it should be oriented so it face the unexposed material.