Hi tyfighter,
I think you may be referring to post #2 here , with some of the most common pain symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them. Low back issues can be from a lack of deep support or too soft or too thick comfort layers. Upper back issues can be from too thick upper layers, causing rounding or excessive sinking, as well as from surface layers that are too hard or an improper pillow. There really are quite a few reasons for symptoms in both areas.
You seem to be getting slightly better results with firmer options in the upper two layers. As soft-firm-medium is your best so far, I would try to use that as a basis for starting and test next by going soft-firm-firm and see if the firmer deep down support was the missing link. If that wasn’t better, I would try medium (Talalay)-firm-medium(Dunlop), going with a slightly firmer top layer and see if that’s better.
You are correct that changing layers so quickly makes it more difficult to truly analyze each configuration, but I understand your back pain.
Hopefully you get a bit more data from those choices and you can see if they move you in a better direction.
Phoenix