Distribution between the overall ellipticity (e_all) and the ellipticity (e_pm) in the proper motion space (left panel), the distribution between the orientations (q_pm) and the ellipticity (e_pm) (median panel), and the effective dip angle difference (|q_pm − q_all|_valid) between the overall orientations (q_all) and the orientations (q_pm) in the proper motion space as a function of the orientations (q_pm) (right panel). Two blue dashed lines in the median panel mark −45° and 45° from left to right, respectively. For the right panel, 30° and 60° are also marked by two blue dashed lines. The red open circles in each panel belong to the same subsample that is the clusters with e_pm ≥ 0.4, about 7% of all sample clusters. The blue-filled circle in each panel represents the cluster NGC 2264, and the green-filled circle marks the cluster Blanco 1. The purple-filled circle in the left panel represents the cluster NGC 752.