(upper panels) Elliptic flow relative to the spectator plane, \vtsp, and to the participant plane, \vtetagap and \vtf, as a function of centrality in \PbPb (left) and \XeXe (right) collisions (bottom panels) Ratios of the elliptic flow \vtsp and \vtetagap to \vtf The dashed (solid) lines show the eccentricity ratios of \eprp (\eptt) to \eptf from the elliptic power model The corresponding eccentricity ratios for \TRENTo are shown as solid bands The error bars (open boxes) indicate statistical (systematic) uncertainties The bin-to-bin uncorrelated uncertainties and the correlated ones are combined for \vtsp results For the ratio \vtspvtf, the ZDC scale uncertainties are shown separately as solid boxes centered at unity on the right side of the lower panels.