Simulated distributions of emission measure vs. temperature, EM(T), derived for the minimum (upper panels) and maximum (lower panels) coverage of cores and for the minimum (on the left) and maximum (on the right) coverage of flares. The contributions to EM(T) of active regions (AR, blue), cores (CO, green), and flares (FLs, red) are shown. We assume a constant surface filling factor of active regions (F_AR ≈ 60%), a filling factor of cores ranging between 4 (upper panels) and 40% (lower panels), a filling factor of flares ranging between 0 (right panels) and 1% (left panels) of the coverage of cores. The crosses indicate the values of temperature and emission measure of the two isothermal components fitting the corresponding spectra.