Link Snap of Child SG to a Standalone SG

Setup:
SG_PARENT

    SG_CHILD1 - 4x 250GB

    SG_CHILD2

The Link SG also has 4x 250GB

symsnapvx -sid <sid> -sg SG_CHILD1 -name SNAP_CHILD_SYNC establish -nop

Snap creates no problem

The issue comes when i try to Link it

symsnapvx -sid <sid> -snapshot_name SNAP_CHILD_SYNC -sg SG_CHILD1 -lnsg SG_CHILD1_SYNC_LNK link - nop

I get the following error:
The size of the Source device is not equal to the size of the Target device

Is this because it's a child storage group?