Originally Posted by Michael Slade
The purpose of the ND patch is to even the light over the entire printing area so it would not be a bad idea to replicate the patch if feasible.
Many NuArc 26-1k(s) units don't have anything to even out the light. My Amergraph ULF-28 has nothing on the tempered glass, but there are patches on the reflector above the glass. I had a 26-1k in the past and it had nothing to even out the light, but the coverage was still excellent at about 20" circel.