/home is for user-specific data, wherever it's coming from or being stored on. The immediate children of
/home often came from other filesystems back in the glory days of NIS (although that was with NFS automounts). It would only seem weird to me if you had personal files mounted on some random directory like an immediate child of
/var or something. Most "best practices" relate to things related to filesystem choice/sizing(e.g reiserfs vs ext4), volume management (e.g giving LV's just enough space to do their job and leaving the rest in the VG for later expansion) mount points are basically "If it's not obviously wrong, and that's where you need the space to be, do it."
In an enterprise environment, you try to mount filesystems where people are most likely to go looking for the files that are stored on that filesystem, or where if they see the filesystem mounted they can infer what the files belong to/are for. This is a personal server, so it's not an issue, but this would probably be fine in enterprise environments as well.
As long as you personally understand the filesystem hierarchy, and have access to the files you're backing up there, you should be good.