File Backup - Symbolic Linking - .directory_pool explodes

I was trying to setup another backup server for a friend based on mine that is running since years.
WS2022 with storage pool and NTFS partition
“Use symlinks during incremantal file backups”: checked
Full file backups: disabled
Incr. file backups: 1 per hour

I compared the settings with my up and running system and it seems to be identical configured.

I configured one directory of one client and had the backup running for several weeks now. (incr. file backup 1/h)
The directory to backup has a size of ~430GB
After that time the backup disk on the server was filled up with a used space of 9,28 TB?!
The source directory itself has not changed in a large manner.

The .directory_pool directory was filled up on the server and I don’t know why.

I do see that the urbackup is creating links but it seems that the directories are not deduplicated.

I am not sure since it is such a long time ago but I think I didn’t had to change anything else for getting each directory exactly one time saved on the backup disk.

I know that NTFS is important.
And I also do know the “Use symlinks during incremantal file backups” is also important. But now I am a little bit lost now why the storage is filled up that much.

BTW: in the web gui under statistics it also says ~432 GB. What does that mean. Are the other files in the .directory_pool not used any more?

Is there something else to configure that I don’t remember any more?

Hope you can help!