What I was trying to illustrate (and obviously didn't do a very good job of it) is that if your pack is too stiff (along your back) it puts a lot of pressure on your shoulders. Contouring the pack (regardless of whether the straps are at a higher or lower angle), is what provides the comfort and reduces shoulder strap pull on your shoulders.
If you look at my pack in the second picture you can see the stress marks in the pack that are caused from pressure pulling the pack back into position (because the Z-lite pad inside is making it stiff). This is not downward weight, my pack is always supported by a waist belt. I've even added the Exodus waist belt to my Burn and always use a waist belt to carry the weight.
The last picture that I included in my previous post show that although the pack may be supported by the guys waist belt, the pack will swing and tug on his shoulders because the pack is not pulled in against his back. I occasionally slacken off my pack straps and let my pack fall back a bit away from my back to get cool air on my back. The weight is still on my waist belt but I sure wouldn't want to carry it for long this way even though the shoulder straps may appear to be attached at a better angle. The straps pull on my shoulders and the pack travels from side to side.
Here's another picture from MLD's site. Ron is wearing the Burn in this picture and the straps wrap slightly around his shoulders but more importantly, he has contoured the pack to fit the shape of his back.