For me, it’s that knob on the right for lumbar. I find most comfort by completely deflating the sac in the seat. I swear, some guys have it full inflated, sticking like a knife into your spine. How is that comfortable? One of the first things I do is use the lumbar support and turn it all the way so the seat isn’t stabbing my back, and deflate it to an almost 0 condition.
Also, the same knob on the opposite side controls vertical backseat height pitch, and changing that does wonders. I’ll adjust it so the top of the seat is just about 1/2” higher than the top of my shoulder. That seems to work great. This adjusts the vertical seat height, but the “side” flank panels of the back seats also move with the seat. By adjusting that, I find a good position for my back.
Every plane is different it seems, but my rule of thumb seems to work for my back.
Another knob I learned, the right side by your thigh. Some guys have that turned fully up. WTF? You like cutting circulation underneath your thigh muscles? I also let that run nearly full down / straight level position. This way my legs have a comfortable position where the seat ends.