Have you played around with the Weight? You didn’t mention it in the post.
What exactly do you mean by “not efficiently”? It seems like you might have some numbers or some graphs to show. If you do, please do. ZS doesn’t know when initiating a connection which connection is going to be big, and which is going to be small. So it might send a bunch of long downloads from the same connection. While true that in the long run, this should even out, depending on the resolution of the data you are looking at, some variation is to be expected.