hey idk who taught you but if you brought it to a professional he/she would set the contact pattern right in the middle. That is the proper way to do it, I have never heard of that 1/3 to the bottom thing. (and before you argue about what the professionals do, keep in mind, I am one)

 

i had this same issue on my old 76 chevy pickup, i had the truck for over 2 years and the entire time i had it the rear end made a squealing sound that was actually kinda loud it had the big corporate 14 bolt rear end and i checked the diff. fluid multiple time and it was fine but i never did figure out what the problem was. someone told it was because the rear end was crooked and sat alittle further back on the driver side then it did on the passenger side, but i didnt think that made sense because the tires did wear unevenly.

 

Is the gears...if there are Richmonds, I had those 3.73 and did the same thing and were putting by the local hot rod shop and feel they were done correctly. I called Richmond and they said to expect at little noise from there gears.. price to pay, i guess