The rear can be super dark, defect for tinting comes into it when you have darker then 35% in cabin area directly infront and to your sides (i.e front window, and two side windows)
Its stupid to have dark tinting anyways I feel it kills lighting drematically and reduces visablity which is a pain in the ass in parking lots, dark weather, dark areas, night etc .. I.E YOU CANT SEE SHIT!
-but ill still get it :S