The option "selected maximum stored configuration per device" to 1 is only for the number of stored device backups that are backed up into the SpectroSERVER database (SSdb).
I believe you are trying to use the Export feature, which is set to Global Synch task which exports all of the configs.
Now that you have all of the configs, you can change the Export feature to just "Export Unique Configurations only" that way only changed configs will be exported.
There is no way to overwrite everyday Global Synch Task exports, but you could do this via CLI script or just export unique configurations as mentioned above.
Best regards,
Glenn