I guess I don't fully understand the context.
The Automatic Miner Discovery should just add new miners, right? But in order to use it, you have to click Add > then fill out criteria as if you were manually adding a new miner. You can't leave the remote agent IP address/hostname blank for instance. But that should be added, when automatically discovered? And would be different for each miner being added.
Please note that the Auto discovery feature only works with ASIC miners and uses the defined IP ranges to search for ASIC miners on the network. Based on this Awesome Miner will update the list of External Miners and if needed also update the IP address of these External Miners in case of IP address changes (MAC address identification feature).
The concept doesn't work for finding Remote Agents or anything related to GPU/CPU miners.
If you have a single site you update the "Local" entry and configure it for automatic discovery. In this case it's you local Awesome Miner installation that will search the network for new ASIC miners and add/update External Miners based on this.
If you use a distributed setup with additional Remote Agents, configured as Remote Proxy, you can also configure each of them for automatic discovery. On each site the Remote Proxy will scan for new ASIC miners and add/update the list of External Miners in Awesome Miner based on this.
The Managed Host represents from where the network scan will be performed. If a Remote Proxy finds an ASIC miner, the new External Miner object will use this Remote Proxy for monitoring of the new miner as well.