Stellar mass surface density (Σ_mass) and effective radii (R_eff) of the star clusters discussed in this work (magenta symbols), along with the following collection of gravitationally lensed star clusters from literature: Sunburst arc (Vanzella et al. 2022), Sunrise arc (Vanzella et al. 2023), Cosmic Archipelago (Messa et al. 2025), and Firefly Sparkle (Mowla et al. 2024). A comparison with local YMCs from Brown & Gnedin 2021 (red contours) and Milky Way globular clusters (Baumgardt & Hilker 2018, blue contours) shows the high surface densities in high-z clusters when compared to local ones (see also the dotted lines marking the constant stellar mass tracks). For the Cosmic Gems clusters, the black symbols refer to the values published in Adamo et al. (2024) assuming z_phot = 10.2.