\jpsi coherent photoproduction cross section ratio for two different energies (\fivenn over \twosevensixnn) as a function of centrality. The data at \twosevensixnn are taken from Ref. . The vertical lines are the statistical uncertainties while the open (filled) boxes are the centrality uncorrelated (correlated) systematic uncertainties Results are compared with theoretical calculations from Ref.  (GG-hs), Ref.  (IIM and GBW) and from Ref.  with updated Glauber calculations from Ref.  (VDM).