Why wouldn't you include bolts?

Certainly using a logbow close up unless very skilled in use could be more difficult and possibly take a bit longer
Small bows (as used by maurauding Mongolians from horseback) can be fired extremely rapidly and close up (again very highly skilled users though)
And would'nt a loaded sling simply be like a cosh very close ?
And wouldn't a scurgar work as a viciously curved knife ?

Perhaps start the other way round. As suggested by others standardly quarter, third or half damage if adjacent but once a level 30 archer (or whatever) the user is considered skilled enough.

Perhaps crossbows should take a bit longer to load. With the exception of two all my completions of ADOM were gnomish archers (crossbow specialists)

Because they operate in a different manner from missiles. And to keep them from being overpowered, I'd make them much weaker than they were in ADoM. After all, unlike a missile, a bolt keeps going after hitting a monster. One of the downsides is the limited choice of target - you can choose one of eight directions, which means that most of the time, you can't use it to hit a monster placed off a diagonal, unless there's a well-placed wall to bounce off (and it's a bouncing bolt).

As I view it, you have your melee equivalent (burning hands and similar), your missile equivalent, and then you have the dedicated magical attack types, the bolt and ball. But both of those would be far weaker than the melee and missile types, to counteract their ability to hit multiple targets.

If I were going to attach a tactic to them, I'd put them in the Melee category, at least.