Trying to solve some low back pain when riding.. Use to have the saddle high and forward caused me to posterity tilt and flex at the low back excessively I have developed my lower spinal erectors from that bad position.. Now I have kinda figured out I needed more setback and lower saddle to rotate the pelvis more forward to line out the low back.. Breathing is so much better in this position too. My low back is still trying to flex but I do have the ability to rotate my pelvis forward much easier since Ive used a selle smp. I use to be umcomfy on every saddle. So thats what probably made me posterior tilt so I can sit on the sit bones better. Selle smp has been the best saddle by far.

Here is a video of me rotating the pelvis, I feel when I do rotate I feel a bit restricted in the hips at the top of the pedal stroke I can only keep it there for a while but not when im putting power out, I feel I have to flex at the spine

https://www.youtube.com/watch?v=0BiCpRbDauM