Distributions of log₁₀(R_e/kpc) for Brightest Group Galaxies (BGGs) in two stellar-mass bins (9.25 ≤ log₁₀(M_*/M_⊙) < 10.75 and 10.75 ≤ log₁₀(M_*/M_⊙) < 12.25), split into two redshift intervals (0 < z ≤ 1.5 and 1.5 < z ≤ 3.7). Star-forming galaxies (SFGs) and quiescent galaxies (QGs) are shown as blue and red histograms, respectively, with skew-normal fits overlaid (dashed for SFGs, solid for QGs). Legends list the number of galaxies and best-fit parameters a, μ, and σ.