Diff-Inc backup is almost of same size as full backup for DFSR data

We have configured NetBackup policy for DFSR data as per the article https://support.symantec.com/en_US/article.HOWTO65638.html.

- There are two schedules configured for backup policy - daily differential-incremental backup & weekly full backup.

- Differential-incremental backups are always almost of same size as full backup, which leads to storage unit getting full very frequently.

Could someone please suggest why are the diff-inc backups of same size as full backups for DFSR folder ? Is there any extra configuration or any specific changes needed to make it work?

Symantec Netbackup Client v7.6.1 is installed on the client & v7.6.1.2 is installed on the server side.

Thanks!