Question about the Sprite mask implemented with the Stencil buffer

Hi. am looking for someone who is familiar with the shaders. So, there is a simple example of what I’m asking about. I have a Plane with the next shader

Shader "Custom/World Fog Of War" {
	Properties{
		_Color("Main Color", Color) = (1,1,1,1)
		_MainTex("Base (RGB) Trans (A)", 2D) = "white" {}
	}

		SubShader{
		Tags{ "Queue" = "Geometry+3" "IgnoreProjector" = "True" "RenderType" = "Transparent" }
		LOD 200
		ZWrite off

		Stencil{
		Ref 1
		Comp notequal
		Pass replace
	}

		CGPROGRAM
#pragma surface surf Lambert alpha:fade

		sampler2D _MainTex;
	fixed4 _Color;

	struct Input {
		float2 uv_MainTex;
	};

	void surf(Input IN, inout SurfaceOutput o) {
		fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
		o.Albedo = c.rgb;
		o.Alpha = c.a;
	}
	ENDCG
	}

		Fallback "Legacy Shaders/Transparent/VertexLit"
}

And also a Sprite with this shader

Shader "Sprites/Occluder1"
{
	Properties
	{
		[PerRendererData] _MainTex("Sprite Texture", 2D) = "black" {}
		_Color("Tint", Color) = (1, 1, 1, 1)
		[MaterialToggle] PixelSnap("Pixel snap", Float) = 0
		_AlphaCutoff("Alpha Cutoff", Range(0.01, 1.0)) = 0.1
	}
		SubShader
	{
		Tags
	{
		"Queue" = "Geometry+2"
		"IgnoreProjector" = "True"
		"RenderType" = "TransparentCutout"
		"PreviewType" = "Plane"
		"CanUseSpriteAtlas" = "True"
	}
		Cull Off
		Lighting Off
		ZWrite Off
		Blend One OneMinusSrcAlpha

		Pass
	{
		Stencil
	{
		Ref 1
		Comp notequal
		Pass Incrsat
	}

		CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#include "UnityCG.cginc"

	struct appdata_t
	{
		float4 vertex   : POSITION;
		float4 color    : COLOR;
		float2 texcoord : TEXCOORD0;
	};

	struct v2f
	{
		float4 vertex   : SV_POSITION;
		fixed4 color : COLOR;
		half2 texcoord  : TEXCOORD0;
	};

	fixed4 _Color;
	fixed _AlphaCutoff;

	v2f vert(appdata_t IN)
	{
		v2f OUT;
		OUT.vertex = mul(UNITY_MATRIX_MVP, IN.vertex);
		OUT.texcoord = IN.texcoord;
		OUT.color = IN.color * _Color;
#ifdef PIXELSNAP_ON
		OUT.vertex = UnityPixelSnap(OUT.vertex);
#endif

		return OUT;
	}

	sampler2D _MainTex;
	sampler2D _AlphaTex;

	fixed4 frag(v2f IN) : SV_Target
	{
		fixed4 c = tex2D(_MainTex, IN.texcoord) * IN.color;
	c.rgb *= c.a;

	// here we discard pixels below our _AlphaCutoff so the stencil buffer only gets written to
	// where there are actual pixels returned. If the occluders are all tight meshes (such as solid rectangles)
	// this is not necessary and a non-transparent shader would be a better fit.
	clip(_AlphaCutoff - c.a);

	return c;
	}
		ENDCG
	}
	}
}

This is a Sprite picture - a black ring with a transparency inside and outside it.
78812-untitled-2.png
And the result is looking like that
78815-18.png

The questions are:

  1. How can I remove this transparent area outside the sprite?
  2. Why this happens?

Thanks for the replies.

You could try to replace outside alpha to black.