Detailed gradient shader

Hello, I have a gradient shader but it is very low definition because it is in the vert constructor, I wrote in vert/frag cg, but how can I make it better?

 Shader "Custom/Spawn" {
 
     Properties 
     {
         _Color ("Color", Color) = (1,1,1,1)
         _HeightMin ("Min Height", float) = 0
         _HeightMax ("Max Height", float) = 1
         _Cutoff ("Alpha Cutoff", Range (0, 1)) = 0
     }
 
     SubShader 
     {
         Blend SrcAlpha OneMinusSrcAlpha
 
         Tags
         {
             "Queue" = "Transparent"
         }
 
         Pass
         {
             CGPROGRAM
 
             #pragma vertex vert
             #pragma fragment frag
 
             float4 _Color;
             float _HeightMin;
             float _HeightMax;
             float _Cutoff;
 
             struct VertexInput {
                 float4 vertex : POSITION;
             };
 
             struct VertexOutput {
                 float4 pos : POSITION;
                 float4 col : COLOR;
                 float4 texcoord : TEXCOORD0;
             };
 
             VertexOutput vert (VertexInput input) {
                 VertexOutput output;
                 output.col = _Color;
                 float vertexHeight = input.vertex.y;
                 if (vertexHeight < _HeightMin)
                 {
                     output.col.a = 1;
                 }
                 else
                 {
                     float alpha = lerp (0, 1, (_HeightMax - input.vertex.y) / (_HeightMax - _HeightMin));
                     if (alpha < 0)
                     {
                         alpha = 0;
                     }
                     output.col.a = alpha;
                 }
                 if (output.col.a < _Cutoff)
                 {
                     output.col.a = 0;
                 }
                 output.pos = mul (UNITY_MATRIX_MVP, input.vertex);
                 return output;
             }
 
             float4 frag (VertexOutput output) : COLOR {
                 return output.col;
             }
 
             ENDCG
         }
     }
 }