It always has driven me nuts that 4 x 5 enlargers do not cover 4 x 5, especially the Omegas. My solution was to have a piece of white milky opal glass cut to fit just beneath the omega mixing chamber. There is enough room. The opal glass will mix the light a bit more and grow the source size just a bit. Because it is glass it is much harder to scratch and it is now a softer light source slightly closer to the negative. It will have more coverage and it will help spread the light- this also reduces the side to side color differences common to Omega diffusers. If you are having glass cut, have the edges polished, this removes jaggy edges and will help keep it from breaking when handling. The other trick to help with coverage issues related to the light source is to use a longer lenses. Incidentally, a dremel and a file are two of my favorite darkroom tools, but since I switched to Durst 1200's I have not had to cut out a carrier, yet. I miss the cheap flat omega carriers, but the durst is worth the expensive of femonegs. Good luck.