PM diagram of the sample clusters, with the RR Lyrae colour-coded by the membership values. The background stars are divided into those that are more central and those that are further out, shown as cyan and grey points. The two-dimensional Gaussian distributions mark the central cluster and field PMs, along with the dispersions (contour lines mark 0.25 − 2σ in steps of 0.25σ), as derived from the GMM method. The diagrams in the lower panels are zoomed in due to the lower dispersion of the cluster PMs.