There's only very small margin from above and in an Airbus presentation it is not recommended. Main thing is FINAL APP mode is designed to fly only between Final Descent Point down to applicable minima. It is not capable of flying any level off segments with altitude constraints before final descent point. That must be done in Des mode.
The To way point must be the FDP is one of the conditions for engagement of APP mode. So if vectored sequencing to FDP(Not beyond) is mandatory.