To make your custom segment more specific/narrow add another custom segment filter. To do this, follow the below steps, after logging into

  1. Click PEOPLE
  2. Click Custom segment tab
  3. Click custom segment nameĀ 
  4. Click Add condition
  5. Select filter specifications
  6. Click search
  7. Click save as custom segment
  8. Select either update custom segment, or save as new custom segment