You know there's an easy fix for that, right?    
Just edit "MDG_strokesDefs.lua" file and reduce the values in the first two lines:   
C:\Eagle Dynamics\DCS World\Mods\aircraft\FA-18C\Cockpit\Scripts\Multipurpose_Display_Group\Common\indicator\MDG_strokesDefs.lua   
Before: 
  stroke_thickness  = 0.8 
  stroke_fuzziness  = 0.5   
After: 
  stroke_thickness  = 0.4 
  stroke_fuzziness  = 0.2