Instead of using file backup to restore files, it would be good for the server to use the IMAGE back ups to create the file tree to be able to restore files.
The above would mean you dont need to back up both IMAGE and FILES, only IMAGES, then when a file is requested it would build the file tree from the stored image and incrimentals. There are a few other large backup companies do this.
Its likely you would need more backend work when creating the tree to look at the file set and revisions, but its way cleaner and the amount of times you need a restore your doung less work in the backup process and this extra work is only done when requesitng a restore.
This would likely mean a new restore method.
Restore type File or Image
If file is selected then dates are shown of all the file trees it can restore from (based on the full and incremental sets), select a date which then builds that tree. This would require mounting of the images INSIDE the server to pull that data, so this might need to be tied in to the Virtualization request thats been on here : KVM/Qemu Suggestion - Feature requests - UrBackup - Discourse