There is No formula
There is No formula. It is Lucky or Unlucky.
It is based on Karma. I know people who got GC in 20 days and still waiting for it for 10 years. I am waiting on it for 5 years now. Do not try to come up with formulas. I and my friend with the same pd filed on the same day. His went to TSC and mine to NSC. He already got his GC 2 weeks ago.