Forgive me I was under the impression we were talking about B747 and A340 (4 eng a/c) not A320.

Seems that all A/C have different rules.
I looked it up in the Perf. manual the other day, there is even a difference between the 737/700 and 737/300. For T/O in the 700 on a dry runway you don't take reverse into account but you do an a wet RWY however on the 300 you take reverse into account on both wet and dry...

Interesting point M&V, particularly if the clearway is the max permissible (ie 50% TORA). Would suggest its not much!