Run standalone server with -c standalone-ha.xml and mod_cluster configured on the same box for a simple load balancing test. Modcluster is not able to detect the as7 instance without explicitly setting the Profiles > ModCluster > Proxies> ProxyList property in console to the ServerAdvertise value from httpd.conf. There should be some sort of indication in the UI or in the server logs when Advertise functionality is not working or fails to work.

Additionally the documentation for modcluster setup and FAQ should be updated to include this note for those troubleshooting their modcluster setups.