Median and 68% confidence interval of the differential contribution to the total characteristic strain signal, based on 2000 Universe realizations, shown across MBHB redshift bins for both circular and eccentric populations. We compare the results at two observer frequencies: 3.1 nHz (left panel) and 27.6 nHz (right panel). The vertical lines represent the median redshift values at which the cumulative contribution (integrating from low and high redshifts, respectively) reaches 5% of the total strain signal for the circular (solid line) and eccentric (dashed line) populations.