I never see any doubles in the opening rollouts, why is this ?

• double 6 is clear to me, 24-18 (2x) and 13-7 (2x)
  
• double 5: most probably 13-3(2x)
  
• double 4 is a doubt: 13-5(2x), or 13-9(2x) and 6-2(2x), or 8-4(2x) and 6-2(2x). I tend to go with 13-9(2x) and 24-20(2x)
  
• double 3: i have no real idea, i go either 13-8(2x) or 6-3(2x) and something else
  
• double 2: i have no idea either, i usually go 6-4(2x) and 1-5 or 13-11(2x) or 13-9
  
• double 1: 6-5(2) and 8-7(2x) ?