Because QoS is enforced on traffic as it egresses the firewall,
your QoS policy rule is applied to traffic after the firewall has
enforced all other security policy rules, including Network Address
Translation (NAT) rules. If you want to apply QoS treatment to traffic
based on source, make sure to specify the post-NAT source address
in a QoS policy rule (do not use the pre-NAT source address).