It's important to get your head around what happens at 50ft on the Airbus. The aircraft enters its flare law, auto-trim ceases and the system memorises your pitch attitude.
What this means in practice is that if your pitch is less and your ROD is more than it should be at this stage it can be hard work to prevent an unpleasant arrival.
Indeed, the FCTM itself says:
Prior to the flare, avoid destabilization of the approach...from stabilized conditions, the flare height is about 30ft.
Personally, I find that ensuring the ROD is sensible and where I want it to be at 50', then beginning a gradual flare just after 30' to be established in the flare by the "retard" call generally works well for me in normal conditions.
Flying the Airbus on the line, I see a huge variation in what people do with the thrust levers during landing, from retarding at 40ft to closing them a millisecond before touchdown.
The FCTM tells you to close the thrust levers
when best adapted.
In my opinion, the problem with closing them too late is that the autothrust remains in speed mode, and if you're not careful it will start adding thrust to try to keep the speed. This can lead to a floaty messy arrival at best.
I have seen guys slowly retard the thrust levers from 30ft to be at idle by touchdown - I think it's mainly the guys who have come off the Boeing who have carried this technique over to the Airbus... I understand what they are trying to achieve by bleeding the power off gently, but from my own observations just closing the thrust levers at about 30-20ft has a similar effect, as FADEC will ensure the engines spool down slowly, and there's plenty of residual thrust.
I agree with the previous poster, gently releasing a modicum of back pressure on the stick just before the aircraft touches down can produce a smoother touchdown, this is particularly noticeable on the A321.