sorry, youre still confused. you only needed to do one of them to make it simpler, instead you did both and made it complex. yes it works, but its not efficient.
the easiest way to think about this is if two containers need tell each other where files are they must have an identical mapping setup.
eg, transmission is setup to save to /downloads/completed/... and /downloads is mapped to /volume1/media/downloads
if you want it to talk to sonarr, and for sonarr to understand you must map /downloads in sonarr to the same place you did in transmission.
if you do that then when sonarr asks transmission where the file is, and it says /downloads/completed/video.mkv then sonarr can see that file in that location because it has the same mapping setup for that.
if for some reason you cannot use the exact same mapping then thats where the remote path mapping comes in. you can tell sonarr that when transmission says the file is in /downloads/completed/video.mkv it should actually look in /downloads/video.mkv
for containerised apps on the same host you have no real excuse for doing it that way - just map the volume the same and be done with it. its more useful with apps that are hosted on different servers or locations. you can tell sonarr (running on windows) that when transmission says the file is in /downloads/completed/video.mkv it should actually look in N:\downloads\video.mkv
the overall simplest method, especially if using a single host, is to use a common root level across all your containers for your media processing, eg i use /media. transmission saves to /media/downloads/transmission/completed, sab saves to /media/downloads/sab/completed, sonarr has root folders for /media/tv/current and /media/tv/ended, radar uses /media/video/movies-new, plex/emby/jellyfin/etc also have /media mapped and libraries set for each appropriate folder.
they all run under the same user, media (or are in the media management group) so they have the appropriate permissions to those locations
it can be a pain to reconfigure everything like this, but its worth it. sonarr can move files instead of copying them (and that may seem pointless but constantly copying 1-2gb files around for no reason is a waste of server/nas resources when hard linked moves are instant and take practically no resources to create). it also makes troubleshooting later on much simpler as well. its all under one volume, not a mishmash of volumes. permissions are simpler. the whole thing ends up making more sense to you.
because its an example for an isolated container so it makes sense. you need a path to pick up downloads from. thats a reminder to make sure you have one.
where it doesnt make sense is if you have a much more tightly integrated setup in mind that will run across several containerised applications on the same host.
think about the above. you can leave it as is but it would be better if you understood why its working that way, and that you have options if you do want to clean it up later.
