Fly by wire aircraft can have a more aft c of g due to their artificial stability. Some even move the c of g aft by pumping fuel into a trim tank in the tail (A330). This saves about 1% fuel.
But don't forget that the air over the tailplane is deflected by the wing. If you want to see by how much, have a look at the gutters over the doors which are generally aligned with the airflow in the cruise to avoid drag. You will see from the pic below this can be considerable.
Another thing to consider with tailplanes is that they often have greater sweep than the mainplane for stability. if the tailplane is affected by compressibility before the mainplane, this could be disastrous for stability. This isn't the case on all aircraft. For example, the B747 has a higher fineness ratio to achieve this.