Shader issue with a 170 upper angle

Hello!

I have a mask by angle shader that work’s fine, but i ‘ getting a disappearing object on angle upper than 179 or -179,

Someone know a way to fix it?

For example when my _Angle value is 1 or -1 object insted to continue rotating it just disappear.

 Shader "Unlit/MaskedBasedOnAngle"
 {
     Properties
     {
         _MainTex("Base (A=Opacity)", 2D) = "" {}
         _Transparency("Transparency", Range(0.0,0.5)) = 0.25
         _Portion("Angle",Range(-1,1)) = 0
         _Size("Size",float) = 5
     }
         SubShader
     {
         Tags{ "Queue" = "Transparent"  "RenderType" = "Transparent" "IgnoreProjector" = "true" }
         Zwrite Off
         Cull Off
         Blend SrcAlpha OneMinusSrcAlpha
         Pass
     {
         CGPROGRAM
 
 #pragma vertex vert
 #pragma fragment frag
  
 #include "UnityCG.cginc"
         struct appdata
     {
         float4 vertex : POSITION;
         float2 uv : TEXCOORD0;
     };
     struct v2f
     {
         float2 uv : TEXCOORD0;
         float4 vertex : SV_POSITION;
         float3 worldSpacePos  : TEXCOORD1;
         float3 objectCenter : TEXCOORD2;
  
     };
     sampler2D _MainTex;
     float4 _MainTex_ST;
     float  _Transparency;
     float _Portion;
     float _Size;
 
     float4 setAxisAngle(float3 axis, float rad) {
         rad = rad * 0.5;
         float s = sin(rad);
         return float4(s * axis[0], s * axis[1], s * axis[2], cos(rad));
     }
  
     v2f vert(appdata v)
     {
         v2f o;
         o.vertex = UnityObjectToClipPos(v.vertex);
         o.uv = TRANSFORM_TEX(v.uv, _MainTex);
         o.worldSpacePos = mul(unity_ObjectToWorld, float4(v.vertex.xyz, 1)).xyz;
         o.objectCenter = mul(unity_ObjectToWorld, float4(0.0,0.0,0.0,1.0));
         return o;
     }
 
 #define TWO_PI 6.28318530718
     fixed4 frag(v2f i) : SV_Target
     {
         float3 v = normalize(i.worldSpacePos - i.objectCenter);
         half4 c = tex2D(_MainTex,i.uv);
         float angle =( atan2(v.y, v.z)/ TWO_PI*4.)+0.5 ;
 
         float t = (angle.xxx / _Size );
         c.a = 1.- smoothstep(0.079,0.08, abs(t - _Portion));
    
         return c;
     }
         ENDCG
     }
     }
 }