Scale and repeat texture without tilling

I need to separate the UV to grids and draw a texture in each grid.
It looks like using tilling and offset to make a texture repeat. But I want to make the texture scale in its grid.

 Shader "Custom/NewSurfaceShader" {
     Properties {
         _MainTex ("Albedo (RGB)", 2D) = "white" {}                        
         _Scale ("Scale", Range(0,5)) = 1.0      
         _SegmentX("Segment x", Float )=5
         _SegmentY("Segment y", Float )=5
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         LOD 200
         
         CGPROGRAM
 
         #pragma surface surf Standard fullforwardshadows
         #pragma target 3.0
 
         sampler2D _MainTex;
 
         struct Input {
             float2 uv_MainTex;
         };
 
         float _SegmentX;
         float _SegmentY;        
         float _Scale;    
         
         void surf (Input IN, inout SurfaceOutputStandard o) {        
         
                     float2 _Diameter=fixed2(1/ceil(_SegmentX),1/ceil(_SegmentY));
                     float2 center = float2(_Diameter.x*floor(IN.uv_MainTex.x/_Diameter.x), _Diameter.y*floor(IN.uv_MainTex.y/_Diameter.y));
                     center+=_Diameter/2;
 
                     float2 _rd=_Scale*_Diameter/2;
         
                     fixed2 uvMask=fixed2((IN.uv_MainTex.x-center.x),(IN.uv_MainTex.y-center.y));
                                         
                     uvMask=(uvMask+_rd)/(2*_rd);
                     uvMask=saturate(uvMask);                        
                     o.Albedo =  tex2D (_MainTex, uvMask);    
         }
         ENDCG
     }
     FallBack "Diffuse"
 }

when I change the scale, a strange line appears at the edge of grids, which the value of uvmask jumps from 1 to 0. The lines are more clear when the scale is less than 1. It works well when drawing colors in each grid.
The only way I found to remove that line is to mirror the UV in every other grid.

                     fixed2 uvMask=fixed2((IN.uv_MainTex.x-center.x),(IN.uv_MainTex.y-center.y));
                     
                     fixed2 indexXY=fixed2(floor(IN.uv_MainTex.x/_Diameter.x),floor(IN.uv_MainTex.y/_Diameter.y));
                     fixed2 dir=1-step(fmod(indexXY,2),0.1)*2;
                     uvMask*=dir;
                     
                     uvMask=(uvMask+_rd)/(2*_rd);    

Have you guys get some other ideas?
Does a fragment shader really run in each pixel?