Well, if there is no straight forward way to do it you might be able to mask it in your post process material by using the CustomDepth pass or the DecalMask pass. But i don’t know what kind of objects you use and if the tickboxes are available for that. Another downside is that you can’t use the masks for other things anymore. I made a thread here concerning a custom masks feature request here: Masks - Feedback & Requests - Epic Developer Community Forums