Quote from FuriantWhat you're talking about is called the Mirror Bar - it handles things like breath, fatigue, and so on. I'm not sure Raven does that, but several other addons, like "Quartz" do.
I have quartz and am using that but I haven't figured out how to unattach it from the cast bar and make it larger. I think at one time long in the past I had it separated from the cast bar during BC but have not been able to redo it and am not sure I can.
I sometimes forget about the breathbar when it is so small. Raven is awesome, and so customizable but I think you are right because I have tried all kinds of settings and cannot find a mirror setting in it.