I have an original D2, not the variable, with all three condenser sets.

The 6+in condensers work fine with both 135 and 150 lenses on the proper cones. The condensers are as close together as possible flat sides out, convex sides nearly touching.

I think you are using the wrong bulb. The PH111 &112 have a long neck compared to other bulbs. A shorter neck like a household bulb has will have the light source improperly positioned, ie too high up, thus causing the vignetting.

Most 135 lenses will cover 4x5 minimally. My Schneider Comparon 4.5 works perfectly from 8x10 to 20x24. The 150 Comparon was moved to the D6 Chromega for color work, but was fine for the D2.