I have built this type of quiver for over forty years, and prefer it to all others.
If you watch his videos, DVD, or on Youtxxx, of the elephant hunt, lion hunt scenes, or one of the other videos, you will see the position of the back quiver, early in his career, and later. The quiver collapses on his back (flat). Notice the top corner is behind the right shoulder, and the bottom of the mouth is below the shoulder. I see a difference between the quiver worn in Africa, and some of the early models.
If you attach the strap below the fold, and 2-3" below the top edge (fold), on the back side, both top and bottom, the quiver will lie flat, and the nocks are easier to reach. If the strap is attached on the fold, the arrows move away from the body. It can also happen if the strap is too tight across the chest, or the leather is too stiff. Personally, I find it harder to to reach the arrows when they are further back (out of position).
If you Google Howard Hill Archer, you will see the positions in the videos. Also, look at the series of Images of Howard Hill. You will see early images, and later images of quivers by Howard Hill.
There is a picture of one made by Howard Hill Archery, showing the strap attached to the fold, and not the back side. The mouth of the quiver is turned out. I feel this type is harder to reach and use.
You will also see several images with the arrows further back (obviously, not for him, but for me it is harder when hung this way). This never seemed to be a problem, because he could still reach the nocks. He attached the strap to the fold, early in his career, and to the back later on.
I prefer the strap on the back, below the fold or crease and below the top edge, the arrows and nocks are closer to the arm and elbow when reaching back.
Depending on your body shape, and size of your chest and arms, you may find it works best in one position over another, proving that one size does not fit all.
Let me know if you have questions.