Iron abundance (left panel) and iron mass (right panel) vs. total mass and their best fits. The symbols have the same meaning as those in Fig. 1. This finding agrees with the trend seen in simulations (e.g., Fig. 11 in Fabjan et al. 2010) toward less massive clusters having lower gas-mass fractions but higher iron-mass fractions, so that the gas is more metal-rich in those systems.