Reach is normally ranked from 1-100. Anything over 100 requires ranged weapons (for a normal-sized person).
Weapons have an effective range of reach. A long pike, for instance, might be useful at 95-100. A longsword might be useful at 45-55.
Some natural weapons (including fists and things) would have no minimum reach.
Some weapons may have a semi-effective range as well. A longsword might be semi-effective down to range 30.
Some weapons may, essentially, be two weapons in one - each with a different range. For instance, a nasty cutlass with a spiked basket-hilt might have a range or 40-50 for the blade and a range or 10-15 for the hilt. Or something.
Range would be modified by height. A four-foot-tall goblin might subtract 10 from his weapon's reach. A big, burly basketball-player-sized barbarian might add 8. A fifteen foot tall giant might add 70.
The thing is - outside of your weapon's range - your weapon can't be used. Thus, a lot of combat would involve maneuvering to keep melee in your weapon's effective range and outside of your opponent's...
Depending on the rest of the combat system this could have some nice effects:
- Big things would be really scary, particularly if they could keep you at a distance.
- Small things could be bad if they got inside your reach, since they'd be effective at that range and you'd be largely limited to trying to push them away.
- Between similarly-sized opponents, small differences in reach still matter - and footwork becomes important.