I would try pic 1, lower back, or something in between that an #2. Try taking the shoulder straps off when you're hanging cause they might cause it to ride up. I would try shortening your tree strap a little also. If we say your knees are at 90 degrees right now, if you make the tree strap shorter it will bring them up to lets say 110 degrees. This is how I sit most of the time. I think from his videos Boswell is even more upright than me. That is why I rely on knee pads so much.
Also, for the tree that you are hanging on, I would hang on the opposite side so I am leaning into the tree. This is way more comfortable (again, knee pads) and that can cause a lot of stress on your back as well.