How can I avoid extra draw calls when my prefab instances have different sorting orders?

I have many prefab instances in my scene, but for a certain reason, I have to display groups of them on different sorting orders, within the same layer.
I get 2 to 4 times the number of draw calls that I would get if they were all with the same sorting order.

Is there a way I can avoid those extra draw calls while displaying them with different sorting orders?

Or maybe a way of creating the illusion that they’re on top of each other while keeping them with the same sorting order?

EDIT: I meant that they have different sorting ORDERS. They are all on the same layer.

You also have sorting order !

If i remember well each sorting layer could have a sorting order from 0 to 32000.

Or maybe just deplace them in the Z axis.