I was playing around with the diffractive object file of young’s double slit experiment from the knowledgeable article, https://support.zemax.com/hc/en-us/articles/1500005575862-The-Source-Diffractive-object.

When I reduced the UDA scale to 0.25 on the source diffractive, I noticed something strange. An artificial aperture is applied to the detector rectangle. Even though you can see rays in the layout striking outside of that aperture. Even stranger is that this aperture is not applied to the Polar detector. See images below.

Can someone explain what is happening. Why is this aperture affecting the raytracing components. I thought the diffractive object just launched the ray angles in accordance with Fraunhofer diffraction theory. It should have no effect after that, yet it seems to.