I wonder what version of SANOS are you using, and if you are using iSLB.
Usually the MDS9000 portal, in reporting the iSCSI targets, lists the "TargetName" but it doesn't insert the optional "text key parameter" of the type "TargetAddress". This is different in case you use iSLB.
You could assign a public IP address to the IPS interfaces only: they are probably a small number and maybe you can find enough available public addresses to avoid NAT-ting just these interfaces.
Another option could be using a VPN tunnel, so you could have your iSCSI initiator virtually part of the same network of the targets, use private addressing for all the devices, and avoid NAT-ting. You probably don't want anyway to have your iSCSI traffic in cleartext on the Internet.