Effect of doping on the octahedra
Doping holes (positive charges) by adding Sr shortens Cu-O bonds
localized holes in stripes implies a coexistence of short and long Cu-O in-plane bonds => increase in Cu-O bond distribution width with doping.
We see this in the PDF: s2 is the width of the CuO bond distribution which increases with doping then decreases beyond optimal doping
Bozin et al. Phys. Rev. Lett. Submitted;