I did a quick search to try and dig up where I remembered reading about how it works, this is the info I found:
Given how old that thread is I don’t know if that line about layering still exists in the game, but what I remembered was a discussion about how the top layer would render over everything else. It may have been comments on a stream though, come to think of it, so unfortunately I can’t point to a clear-cut answer.
I guess the best thing at this stage is to page one of the dev team who can explain the system better?