Right, that is my point.
Perhaps, yes. However, there is also the fact that layers assigned to the small mix would still need to be layers that were not assigned to the main mix. This is the only reason I mention using a layer positioned and scaled instead.
When thinking about it now, I was proposing a way that might be simplest. I change my mind now realizing it's just as simple or easier to do the submix on top. It's just not something that can be changed from the controller (yet).
DMX controllable submixes would be nice and something I hope for soon.