The Real User Experience Monitoring (RUM) is a new approach adopted to provide specific control on IT services and systems, allowing to analyse the performance and response time that the user really experiences.
If you have an application behind a load balancer and the probe is between the client and the load balancer, the RUM retrieves only the connections between client and load balancer but it is not able to distinguish each single node behind the load balancer.
That means that you lose a level of details and the latencies are calculated as the average among all nodes served by the load balancer.
To avoid this limitation, you can add an http header tag from each server behind the load balancer. This tag contains the identifier of the server, the probe recognizes the tag and the RUM assignes the latencies to the single server instead of to the load balancer.