ip back is the IP address of the vif interfaces for a ProxyVM.
It is the address that downstream qubes see at first hop upstream, and is
default gateway for those qubes, (and default nameserver too.)
You misunderstand the use of --raw-data: it's not for VMs.
--raw-list just gives you names, --raw data gives you values for specific
keys:
qvm-ls --raw-data netvm will show ordered list of the netvms for each VM.