Fit to the classic FP (Eq. (1)) built with a sample of 35 secure ETGs selected as members of the galaxy cluster PLCK-G287. The aperture-corrected central stellar velocity dispersion (σ_e8) is expressed in km s⁻¹, the surface brightness (I_e) in L_⊙ pc⁻², and the circularized effective radius (R_e) in kpc. The solid black line is the projection of the best-fitting plane, and the dashed and dotted red lines indicate the 1 and 4 standard deviation intervals, respectively. Green squares indicate the two objects that are found to be outliers of the M^⋆ and f_e^⋆ HPs.