The advanced tokamak (AT) scenario (defined by high fusion efficiency with operation close to steady-state conditions) is one of the most promising ways to achieve the steady-state operation in the forthcoming fusion power plants. The motivation in AT identity plasma experiments was to study the forming of ITBs and steady-state properties. The experiments in JET and JT-60U in 2008, described (technical details and fulfilling the main goals) in publications, were the first experiments where the global plasma parameters and profiles were matched between two similar-size tokamaks with reverse q and the goal of the high bootstrap fraction. The main goal of this paper is to understand the most significant differences between two approximately same size tokamaks, JET and JT-60U, and study the time evolution of the plasma current density and q by predictive current diffusion simulations.