BIT appears to do Full backups every run

I have recently started using Back In Time
Back In Time 1.0.34
on Linux Mint 17.3, Cinnamon Desktop
on Ubuntu 14.04 LTS

I now have three daily backups
It appears to be doing Full backups every time.
I have around 600GB available for backups
I was anticipating being able to keep more than 3 backups with BITs snapshot techniques.

I backup to a Synology NAS device with a Share available both as Windows/CIFS
and NTFS
It is mounted on my Mint system at /mnt/volume1/Backup
The destination in BIT is set to
/mnt/volume1/Backup/JGStuff

Scanning the Backup folders with DiskUsageAnalyzer

20160418-000003-713 33.6% 233,1GB 93789 items
20160417-000002-653 33.2% 230,6GB 93604 items
20160416-202405-761 33.2% 230,6GB 93603 items

We can see that each backup is ~230GB
Which is consistent with the total volume of data in my home folder (less exclusions)
I am pretty sure I have not changed 230G of data every day
I was expecting so see a first backup of something under 300G
Then small backups of the daily changes

Is it possible that the NAS box, or NFS mount is somehow preventing the Snapshot technique from working?
Or that the hardlinks while having little content, report the full file size, which is confusing the NAS?

Thanks for any comments or advice.