Redshift evolution of the mean BH mass as a function of the mean bulge effective radius of the host galaxy, averaged over 29 merger tree realizations with 1σ error bars at few selected redshift, for the reference model (black solid line), and the model with |$\dot{M}_{\rm accr} \le 20 \, \dot{M}_{\rm Edd}$| (orange solid line). Grey circles represent data for local galaxies, with the empirical fit (grey dashed line) given by Sani et al. (2011).