In some deployment of Cisco Expressway series, the Expressway-C and Expressway-E built a Firewall Traversal Connection with Expressway-C pointing to the Public IP 41.1.1.21 of the Expressway-E.

Since the ASA-E is configured with a static NAT so that the Expressway-E is reachable for MRA feature, the problem is that the traffic initiated by the Expressway-C to Expressway-E will be routed to the outside and will never end up at the Expressway-E

This is why we need #NAT Reflection on ASA-C.