Dependence of the 511 keV line intensity in the disk (top) and the bulge (bottom) as a function of the choice of the disk extent (1σ Gaussian width value). Line intensities are shown as shading, see scale on right-hand axis. Overlaid are the uncertainty contours for the disk size, as derived from the maximum likelihood fits in the grid-scan. See Appendix A.3 for more details and other parameter impacts.