I guess it depends on the rider's anatomy.

I used to be on the ball of the foot. Until I started having knee pain. I went to slightly behind the ball of the foot and finally settled to having my cleats right in the middle of the range of where you can install them. Thats when all forms of knee and back pain went away along with proper adjustments to everything else, of course.

You are having back pain because you raised your seat instead of lowering it. As you move the cleat back you are increasing the distance between you and the pedals just like if you move your seat back. Raising the seat made it worse, hence the back pain.

As I moved my cleats back I lowered my seat the same amount of distance ie, moved the cleats 5 mm = lower the seat 5 mm.