Why is object with 384 verts and simple shader not getting batched?


I have a problem regarding the batching of an object (384 verts) with a simple Vertex Colored Shader and no lights.
Each instance of the object adds one drawcall.
I’m using the following shader:

 Shader "Custom/Vertex Colored" {
 Properties {
     SubShader {
             Pass {
                     ColorMaterial AmbientAndDiffuse

Why is it not getting batched? I’m far below the vertex limit and the shader is only using one pass, right?

Edit: Ok, so I reduced the vertices of the object to 300 (deleted a few faces for testing purposes) and now the instances of the object are getting batched. This means that there have to be 3 shader passes because the vertex limit for dynamic batching is 900 vertices per object, right? Why does a simple vertex color shader cause 3 passes?
What can I do about it? It would be difficult for me to only have 300 vertices per object…

if all else fails, reduce verts. it will be worth it.