I use my D2 (DII? - I've never looked to see which one I have) with 35mm, 6mm square, and 4x5.
In all cases, with Omega neg holders, I have stray light, either from between the neg holder plates, or between the holder and the bottom of my Aristo V54 head, or often both. It doesn't matter whether film extends out beyond the edges of the holder or not.
To block the leak between holder and light head, I slide down an old black terry cloth head sweat band and snug it to the top of the neg holder, but I've never figured out a convenient way to block the crack where light comes from between the two holder plates. Anyone have a solution for this? Something that doesn't have to be applied every time the neg is changed?