Which way should I go with pinion angle ??????????????????????

I do have a question about the factory settings. I remember when I set up the rearend I measured the angle of the spring perches on the stock axle and they were at 5* nose up. I have read a lot of posts where other people took * measurements of their factory installed perches and they were all around 4* or 5* nose up from the factory. This has me puzzled. Why were they set like this from the factory?