Bruce381,
I think that you have answered my question. I wanted to know if the add pack was different due to the viscosity of the final formulation. As in - do oils with a final "thin" viscosity require more boundary lubricants for example than oils with a final "thick" viscosity. (I had assumed that the viscosity of each component affected the final viscostity.) On the other hand, I had no idea as two wether the add pack strategy had to be different for thicker vs thinner final formulations.
It sounds like 5W20 may require a little more something than the more viscous grades. I had guessed that the ends of the grades may be different 20wt vs 50 wt, but that the intermediate grades would be somewhere between the ends. From your post, I think I hear that most oils are supplemented similarly and that 20wts may have crossed some threshold that requires more additives. I'm still not clear about that though.