Originally Posted by
genejockey
I find that a cm of difference in setback actually makes a huge difference - 4.6cm setback and I can ride for 5 hours with no back issues, but 5.6cm of setback and I end up with a lower back ache.
What I tried to highlight was that there is a zone of more than 2 cm on the longitudinal axe of the saddle (maybe max 3-4 cm for selected saddle forms) where it is still large enough to support the seat bones. Therefore, the body can "silently" compensate for an error of +/-1 cm in set back setting, by self positioning in the "sweet spot" on the longitudinal axe of the saddle.
By contrast, every cm of saddle height error will translate in altering of the knee angle, with no margin for body self adjustment.
Maybe your saddle is already at the back limit (assuming that "-" means back), so the body has no margin left to compensate further back