I recently installed a Givi E52 box on my '07. I used to own an '05 with the Yam Box. The E52 Box definitely allows the passenger to lean back, where the Yam box didn't. But I won't recommend ordering the Givi Backrest or your passenger will be sitting nearing straight up (and the backrest pad isn't very comfortable).
I'm currently searching around for a thinner backrest pad for my E52 box, to provide a bit more comfortable for my passenger, yet still maintain the nice 'lean angle'.