Is it possible to keep .VIB files longer than 1 week?

[HiHoItsOffToWorkWeGo]

We've got a backup copy job which runs every 4 days to copy data to long term storage off site over a WAN.
Every time it runs it seems to perform a "full backup file merge", where I presume it merges the .VIB files it just created into the .VBK files already present.
Is there any way to make the backup copy job perform this merge less frequently, for example once a month, rather than every backup?
I want to take advantage of the space efficiencies offered by keeping a .VIB file around for longer, and reduce the frequency of the merging (which I assume is the process to create the Synthetic Full backups).

[Mildur]

Looks like you have configured only "retention" and not GFS backups.
With only retention configured, veeam uses a forever forward incremental chain, which means, it must merge every day.

If you configure weekly GFS, veeam will use a forward incremental chain. With this setting, no merging will happen (since V11).