CanvasRenderer + shader clipped Material

I have spent all day on this and can't figure out the math to make this work.

I have a custom Material that includes the shader seen below. The shader makes it so that the mesh will not draw (because the alpha is set to 0) outside of the range specified.

When I use the shader on game object without a CanvasRenderer and just a normal Mesh + Material, I get the behavior I expect (although it seems to like local coordinates, not world). When I use a CanvasRenderer and set the Material on it the clipping works, it just clips in places I can't understand and seems to be tied to the world coordinates.

Is there something I am not accounting for? Is my shader messed up?

Basic Game Objects with Mesh (works):
Here is an example of the basic Mesh (the two lines are the meshes, each with the custom Material applied and setup for that plot). As you can see, the lines are clipped to the plot background (they extend out in both directions, but you can't see it because the shader is working "correctly"):


CanvasRender (broken):
Here is an example of the same shader applied to the plot lines using a CanvasRenderer:


Shader:

Code (CSharp):

1. Shader "Test/Simple Color With Alpha Clip"
2. {
3.    Properties
4.    {
5.       _TintColor ("Tint Color", Color) = (1,1,1,1)
6.       _Clipping ("Clipping", Vector) = (-1, -1, 1, 1)
7.    }
8.  
9.    SubShader
10.    {
11.       Lighting Off
12.       ZWrite Off
13.       Cull Back
14.       Blend SrcAlpha OneMinusSrcAlpha
15.       Tags {"Queue" = "Transparent"}
16.       Color[_TintColor]
17.       Pass
18.       {
19.          CGPROGRAM
20.          #pragma vertex vert
21.          #pragma fragment frag
22.          #include "UnityCG.cginc"
23.        
24.          struct appdata_t
25.          {
26.             float4 vertex : POSITION;
27.             half4 color : COLOR;
28.          };
29.        
30.          struct v2f
31.          {
32.             float4 pos : SV_POSITION;
33.             float2 worldPos : TEXCOORD1;
34.             half4 color : COLOR;
35.          };
36.        
37.          fixed4 _TintColor;
38.          float4 _Clipping;
39.        
40.          v2f vert (appdata_t v)
41.          {
42.             v2f o;
43.             o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
44.             o.color = _TintColor;
45.             o.worldPos = v.vertex;
46.             return o;
47.          }
48.          half4 frag (v2f IN) : COLOR
49.          {
50.             half4 col = half4(IN.color);
51.          
52.             if(IN.worldPos.x < _Clipping.x) col.a = 0.0;
53.             else if(IN.worldPos.x > _Clipping.y) col.a = 0.0;
54.             else if(IN.worldPos.y < _Clipping.z) col.a = 0.0;
55.             else if(IN.worldPos.y > _Clipping.w) col.a = 0.0;
56.          
57.             return col;
58.          }
59.          ENDCG
60.       }
61.    
62.    }
63.    FallBack "Unlit/Transparent"
64. }

Any thoughts, ideas, comments are welcome!