UL of the maximum CR to thermal pressure ratio, X_CR, max. = max(P_CR(r)/P_th.(r)), within the inner 20 kpc of the cluster for different proton spectral indices. Two different CRp spatial distributions were considered for a set of CRp spectral indices. The blue ULs are the result of the magnetic confinement approach (Sect. 4.2), and the orange ULs are the result of the steady-state approach (Sect. 4.3). The prediction by Jacob & Pfrommer (2017a) is also shown, in dashed black.