DepthPass draw call do not batch correctly

I'm having a Sprite shader with a ShadowCaster pass which causes the DepthPass draw call to not batch correctly.

I've created a custom shader based on the Sprite-Default shader and added a ShadowCaster pass to it and changed the render queue to Geometry so that it can write to the depth buffer and use the depth texture in post effects such as Depth of Field.
The depth pass runs, however, the order in which the draw calls are performed is not the same as the drawing order of the renderers in the scene, and therefore dynamic batching is very prone to break on a lot of cases.

Any ideas on what is causing this behavior? I'll post the shader I'm using here:

Code (CSharp):

1. Shader "Sprites/Default-ShadowCaster"
2. {
3.     Properties
4.     {
5.         [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
6.         _Color ("Tint", Color) = (1,1,1,1)
7.         [MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
8.         [HideInInspector] _RendererColor ("RendererColor", Color) = (1,1,1,1)
9.         [HideInInspector] _Flip ("Flip", Vector) = (1,1,1,1)
10.         [PerRendererData] _AlphaTex ("External Alpha", 2D) = "white" {}
11.         [PerRendererData] _EnableExternalAlpha ("Enable External Alpha", Float) = 0
12.  
13.         [PerRendererData]_Opacity("Opacity", Range(0,1)) = 1
14.         [PerRendererData]_Cutoff("Depth Alpha", Range(0,1)) = 0.5
15.     }
16.  
17.     SubShader
18.     {
19.         Tags
20.         {
21.             "Queue"="Transparent"
22.             "IgnoreProjector"="True"
23.             "RenderType"="Transparent"
24.             "PreviewType"="Plane"
25.             "CanUseSpriteAtlas"="True"
26.         }
27.  
28.         Cull Off
29.         Lighting Off
30.         ZWrite Off
31.         Blend One OneMinusSrcAlpha
32.  
33.         Pass
34.         {
35.         CGPROGRAM
36.             #pragma vertex SpriteVert
37.             #pragma fragment SpriteFrag
38.             #pragma target 2.0
39.             #pragma multi_compile_instancing
40.             #pragma multi_compile _ PIXELSNAP_ON
41.             #pragma multi_compile _ ETC1_EXTERNAL_ALPHA
42.             #include "UnitySprites.cginc"
43.         ENDCG
44.         }
45.  
46.         Pass
47.         {
48.             Name "DEPTHCASTER"
49.             Tags{ "LightMode" = "ShadowCaster" }
50.             Offset 1, 1
51.  
52.             Fog{ Mode Off }
53.             ZWrite On ZTest LEqual Cull Off
54.             Blend One Zero
55.  
56.             CGPROGRAM
57.             #pragma vertex vert
58.             #pragma fragment frag
59.             #pragma multi_compile_shadowcaster
60.             #include "UnityCG.cginc"
61.  
62.             uniform sampler2D _MainTex;
63.             uniform half4 _MainTex_ST;
64.             uniform fixed _Cutoff;
65.             uniform float _Opacity;
66.  
67.             struct v2f {
68.                 V2F_SHADOW_CASTER;
69.                 float4  uv : TEXCOORD1;
70.             };
71.  
72.             v2f vert(appdata_base v)
73.             {
74.                 v2f o;
75.                 TRANSFER_SHADOW_CASTER(o)
76.                 o.uv.xy = TRANSFORM_TEX(v.texcoord, _MainTex);
77.                 o.uv.zw = v.texcoord;
78.                 return o;
79.             }
80.  
81.             float4 frag(v2f i) : SV_Target
82.             {
83.                 float a = floor(0.99 + _Opacity);
84.                 fixed4 texcol = tex2D(_MainTex, i.uv.xy);
85.  
86.                 clip(texcol.a * a - _Cutoff);
87.  
88.                 SHADOW_CASTER_FRAGMENT(i)
89.             }
90.             ENDCG
91.         }
92.     }
93. }
94.