I think the fronts are always tinted to legal limit but if you are willing to accept responsibility for illegally tinting the fronts further, it does help if the rears are noticeably darker and then when looking at the car, it seems there is still a considerable difference and the police are less likely to pull you for it.
Dark headlining and dark rear tints do dull the cabin which then means there is less light coming through the fronts when you look at it.