@Gavin666 I have been trying to figure out the sizing myself (I am interested in the indigo version) and compared Self Edge's measurements on the 292 to the collab cpo. For my size range they are pretty close to each other yet different than the measurements on the Iron Heart site. Based on the different measurements I would guess that a medium in the indigo version would fit similar to a medium in the 292 on me (i.e. as a shacket rather than a shirt).
I think for the best guess, find your size in the 293OD on the Iron Heart site and then see how Self Edge's measurements for the 293OD and the SEXIH25-CPOOD compare. I bought the 293OD in a large as I wanted to wear it as a shacket and based on Self Edge's measurements I would buy the same size in the SEXIH25-CPOOD for the same fit.
I hope this makes sense as I know my explanation is a bit convoluted. Not fool proof by any means but probably a good enough guide assuming that Self Edge's measurements for both the 293OD and the SEXIH25-CPOOD are consistent across those pieces.