Help with true mirror like reflections with a cubemap

Im trying to make a true mirror with a cubemap. is there a way to make a shader that will give me a flat mirror like reflection with a cubemap. i need the cubemap to zoom out as you back away from the mirror in stead of zooming in.

 

this is what i have to start with simple reflect shader

Code (CSharp):

1. Shader "Mirror"
2. {
3.     Properties{
4.     _Color("Main Color", Color) = (1,1,1,1)
5.     _ReflectColor("Reflection Color", Color) = (1,1,1,0.5)
6.     _MainTex("Base (RGB) RefStrength (A)", 2D) = "white" {}
7.     _Cube("Reflection Cubemap", Cube) = "_Skybox" { }
8.     _BumpMap("Normalmap", 2D) = "bump" {}
9.     }
10.  
11.         SubShader{
12.             Tags { "RenderType" = "Opaque" }
13.             LOD 300
14.  
15.         CGPROGRAM
16.         #pragma surface surf Lambert
17.  
18.         sampler2D _MainTex;
19.         sampler2D _BumpMap;
20.         samplerCUBE _Cube;
21.  
22.         fixed4 _Color;
23.         fixed4 _ReflectColor;
24.  
25.         struct Input {
26.             float2 uv_MainTex;
27.             float2 uv_BumpMap;
28.             float3 worldRefl;
29.             INTERNAL_DATA
30.         };
31.  
32.         void surf(Input IN, inout SurfaceOutput o) {
33.             fixed4 tex = tex2D(_MainTex, IN.uv_MainTex);
34.             fixed4 c = tex * _Color;
35.             o.Albedo = c.rgb;
36.  
37.             o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
38.  
39.             float3 worldRefl = WorldReflectionVector(IN, o.Normal);
40.             fixed4 reflcol = texCUBE(_Cube, worldRefl);
41.             reflcol *= tex.a;
42.             o.Emission = reflcol.rgb * _ReflectColor.rgb;
43.             o.Alpha = reflcol.a * _ReflectColor.a;
44.         }
45.         ENDCG
46.     }
47.  
48. }

 

If you want to get a nice reflection on a flat surface using a cubemap, you must create a reflection probe, enable https://docs.unity3d.com/ScriptReference/ReflectionProbe-boxProjection.html and adjust the Box Size and Box Offset to create a rough approximation of the scene depicted by your cubemap and then sample this reflection probe in your custom shader (because otherwise the sides of the cube are infinitely far away and the flat surface will reflect only a tiny part of the cubemap). How to do so you can learn here: https://www.bitshiftprogrammer.com/2018/11/reflection-probe-custom-shader-tutorial.html