Distribution of the 24 best-fit M₅₀₀ obtained from the thermal pressure profile fits with η_T free. We present the average mass of the sample for fixed UPPs from the literature, shown with circles and diamonds for the cases where η_T is free in the fit and fixed to η_T = 1.05, respectively. We also show the $M_{500}^{\mathrm{fit}}$ distributions and the average masses obtained from the joint fits of the UPP and individual cluster masses, with η_T and σ_int free in the fits. Different colours indicate results corresponding to the parameters specified in Table E.1 and our three results assuming different δ values. The horizontal dashed line indicates 8.5 × 10¹⁴ M_⊙ as a reference, with the shaded area corresponding to a 10% dispersion around this value.