I_{CO(1 − 0)} versus I_MIRI770/I_MIRI1130 ratio. Top: symbols follow the same convention as in Fig. 3. Middle: symbols are colorcoded by the size of the CO cloud derived in Section 3.2; while circles are CO clouds with size larger than 100 pc, stars correspond to those smaller than this limit. The legend on the bottom panel contains the values of the Pearson r_p for the two groups. The vertical dashed-dotted red lines mark the point log(I_MIRI770/I_MIRI1130)≈0.56 where the scatter of the CO–F770W/F1130W relationship increases significantly (see Section 4.2). Bottom: same as middle panel but colorcoded by the projected distance of the CO cloud respect to the optical center.