We are discussing, trying to envision what you mean, and I think it will probably be necessary to see a concrete example, for us to be sure we understand it.
My instinct at this point is to say, you are using this complicated approach to accomplish what may be natively possible in bella without workarounds, using a different methodology. Specifically, and we went to great lengths to make this happen, opacity is pervasive in how it is exposed in bella materials, and specifically in the blend material.
That is, each material has its own global opacity, and then there is a second opacity applied to it when it is referenced in a blend material. I cannot say for sure, but it may be that you can accomplish what you want by making use of material opacity, blend material ordering, and the per-material opacity applied to each material in the blend.
So if you can provide a concrete (but hopefully as simple as possible) example, along with maps, I’ll take a look and see if/how I would accomplish it in bella.