According to the AD&D Combat and Tactics supplement, weapon reach should generally be based on creature size. Of course, this can be adjusted for balance purposes and due to animation issues.

Size           Weapon reach

Tiny       (T)      0
Small      (S)      1
Man-sized  (M)      1
Large      (L)      2
Huge       (H)      2
Gargantuan (G)      3

Note: creatures of L size or larger should probably have rr#bump = 1
