Not Understanding Machine Region

I’m not understanding the Machine Region setting in MeshCam (note I’m trying V7 Beta). Previously, I added supports in MeshCam but this time I added it to my model – I’m cutting out a spindle fan that one of the user’s here was generous enough to share.

What’s happening is that when the job is run, the support are cut through. Is this because I intersected the supports with machine region vs carrying them out to the edge? If I had made the region larger then it would of done the right thing?