Comparison of observed nebula sizes with theoretical Strömgren radii (Sect. 5.2). The top four panels (2 × 2) show, individually, r versus the Strömgren radius r_str for r_circ (HST), r_mom (HST), r_circ (MUSE), and r_mom,deconv (HST), respectively. The bottom panel overlays all four measurements. In every panel, points are binned at equal intervals in r_str; symbols mark bin medians and error bars indicate the standard deviation of values within each bin. The y = x relation is shown as a dashed black line (with faint dotted offset guides in the overlay).