Thanks for the reply. That's what I suspected. Things start to get out of whack as soon as I have a few sprites from other atlases (units, animated buildings that couldn't fit into the main building atlas) drawing in between other layers. But knowing how it works I can at least try to minimize how often that happens, to an extent.
Is there any way to control what order things are drawn within the same draw layer? This must be happening somewhere, but I suspect it is deep within Unity and unaccessible? For instance, if I had all of ATLAS0 drawing at layer 10 and then had some way of determining what order within that layer each sprite was drawn, it seems like I could make significant draw call improvements. But the best I can tell is that Unity draws them in the order they were first instantiated (I think). If that is the case, my buildings can all be dragged around and moved by the user so that won't help me. Any idea how one might access that order and modify it? Is it even possible? Thanks.