Best setup for Remote Logic and Back to My Mac

I have two iMacs and a Mac Mini which are always on, and I would like to be able to log into any one of these remotely. I have iCloud and Back to My Mac enabled on all three, but it seems they only reliably show up in my Shared sidebar if I am on the same network as them. (The Mac Mini and one of the iMacs share a network. The second iMac is on a different network.) Is there a configuration or additional setting I may have missed? FWIW, I have File Sharing, Remote Login, and Remote Management all turned on on all machines.