Maximum shifted individual BH mass of an initial 55 M_⊙ BH in a stellar cluster with total (stellar) mass M_★ = 10⁶ M_⊙, for cluster sizes representative of the observed Cosmic Gems proto-stellar clusters. We assumed an initial gas-rich cluster with total M = 3 ∙ 10⁶ M_⊙ and star formation efficiency ε = 0.35 at low metallicity. The lower x axis is the final (after gas depletion) Plummer radius, to be compared to the half-light radius of the observed stellar clusters, and the upper x axis is the half-mass radius of the initial gas-rich cluster.