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