I have no idea what the point of a staggered setup on a AWD vehicle is either to be honest ... probably just aggressive looks.
Anyway, the back wheels are wider (to accommodate the wider tires). You will be perfectly fine running same size tires all around: just keep in mind that the back tire will be stretched more ... perfectly fine if you don't mind it like that.
I run 235/40 all around (7.5 inch wide rim in the front and 8.5 in the back):
edit: notice the difference: sidewall sits flush in the front and has stretch in the back