When I used to print with light or bright metal coloured negative holders in my Ilford Multigrade 400 equipped Omega D6 enlarger, there would be an area of reflection and refraction outside the image area, which I rather liked, and would often include in my prints.
This is the full frame of the negative carrier, which does slightly crop the image area of (in this case) a 35mm negative. The easel arms are placed on the paper outside the imaged area, leaving some white paper between the image and the easel arms. No filed out carrier necessary:
The effect is slightly different, but still present, when larger medium format negatives are printed in the same full frame way. I expect that it is at least partially related to using a larger than necessary 4"x5" diffuser in the Multigrade head.