3D Multi Mesh render ordering does not follow z values

I am making a top down 2D RTS. Initially I used multimesh 2d for rendering but I had problems with render ordering as each mesh held its initial rendering order and there were no trivial solution to do dynamic y sorting for multimesh renderer. So I switched to 3d multimeshes with the idea that I may order the meshes using their transform.origin.z values. Which also did not work. You can see in the screen shots below (I have used perspective camera mode to show that the z vlaues are indeed different, normally I use the orthographic),

This looks ok but

when I reverse their z ordering the meshes that have lower z values are smaller but still rendered on the meshes that have higher z values.

Hence in 3d mutliimeshes the initial mesh render ordering is held and it does not care about z values. How can I change the rendering order?