I tend to use rsync to backup my system ( including VMs) thanks an anoying bug . Turns out, this would sync the entire sparse file, expanding from 11gb on disk to 64gb on target system.
To "fix" this I now use qcow2 for disk image, based of instructions from here.
- Move existing images to qcow2 , if not done. This also would allow us to use snapshots via virt-manager 
- Fill VMs with zeros to allow them to be compressed
- Shut down the VMs, and run from host