FxM show 0 milliseconds for client time metric which affects the overall End-to-End time metric.
When FxM is positioned behind a load balancer or one that also acts as a reverse proxy, the FxM system will basically measure client delays to the load balancer. For FxM to actually have any measure of Client Time, the appliance have to see TCP ACKs coming back from the end-user. The load balancer does not necessarily forward those directly to the back end web server. At least not in their original form or at the time they arrive.
This is a long standing known fact regarding FxM. To measure the end-user delays, position FxM in front of the load balancer. For a more accurate measurement of the back-end delays, position FxM behind the load balancer. To capture both end users delay and back-end delays – deploy two FxMs - one in front and one behind the load balancer.