I can't imagine how the inside of the rear window ices up so much that the electric defroster can't melt it, at least enough to loosen it so the rear w/s wiper can clear it. On my Compass, usually the rear melts off faster than the front does.
To OP Dakota: if you've only got 3" clear to see out of, you shouldn't be driving at all. Around here the police will make you clean it off if you're lucky or write you a ticket if you're not so lucky. If you're really unlucky the coroner gets involved.