Description of proxy load balancing and ServerActive parameter should include a few useful details:

• It's possible to set ServerActive to a Zabbix server address, then the server will redirect the agent to a proper proxy if a proxy group monitors this host
• ServerActive doesn't mention proxy groups at all. Moreover, this sentence "More than one Zabbix proxy should not be specified from each Zabbix server/cluster." is not true for proxy group setups. We should mention proxy groups and add an example.