How to Reduce B2D Backup Size

BE 2014 on server 2008.. What is the best way to reduce the size of backups? We currently use full/incremental backup (full once a week incremental every 2 days). We cant use deduplication as that option has to use a local drive. We currently use a 9TB NAS device for backups. We use software compression and keep backups for 2 weeks instead of 4. Whats the best way to reduce backups size?