Im not the legal expert on this but I was pretty sure that any kind of tint, even light smoke/grey on the front side windows, when put over the original factory tint, will go below the legal light transmission amount.
Maybe coppers wont make such a fuss if they see you driving around with a lighter tint, but I dont think if you *were* actually stopped by the police you would get away with it.
Im still doing it anyway, I fancy medium smoke all round. Except the windcreen obviously. And a limo tint on the sunroof.