I noticed differences in using a black collimator enclosure verses a white enclosure. You get much better results with a white lambert than black Lambert material, which is to be expected, however it is black in Thomas’ original scene.
I also had focus issues in my test and possible other material problems. That was version 0.0.16 as well so need to check your bsz with version 19.0.
I’ve left the TIR validator scene running on two rendernodes, so will combine those in the morning and post the render.