The worst fighting is to the north of the city, in the Jolan district.
This is where a lot of the fighters have been based.
Incidentally, it is also where US security guards were ambushed in April, leading to the first siege of Falluja.
I think it is misleading to say the US controls 70% of the city because the fighters are constantly on the move.
They go from street to street, attacking the army in some places, letting them through elsewhere so that they can attack them later.