Hi, you guys. If you will permit a mere lightweight A320 person to add to your very interesting discussion, I think it can be boiled down thus:
The OVW increment is due to the landing technique demanded by the OVW Landing QRH.
THE WT increment is due simply due to the aerodynamics of putting on weight.
Thus, both apply.
I've just had a trawl through my FCTM about the subject - and, jeez, my head hurts. As a matter of supreme indifference, I had a look at the example, guessed at circa 2000m and, guess what, they made it 1850m. I don't advocate taking that line for real, but they sure have made it time consuming!
Thanks for the discussion guys.