[Spaceships] 'Triple' bomb size instead of triple ammo count?

[Kale]

If we assume that the bombs are mainly kinetic kill cluster, then a cylindrical bomb makes sense; a long core of explosive around a bunch of ball bearings or penetrator darts arranged in a cylinder. As the bomb approaches the target it bursts and creates a moving cloud of projectiles. Since it doesn't have engines, fuel, or much of a guidance system there is more room for darts or ball-bearings.
The cylinder allows an even dispersal of the cloud of penetrators.
In the case of a single solid penetrator, again a cylinder makes sense as it allows a narrow aspect ratio. This would be handy for bombing ground targets as it would reduce atmospheric friction.
Given the two above assumptions I'd say it should be straightforward to have a triple-damage bomb the same size as a regular missile. Either it has more darts or more solid mass for impact. One downside is that without engines the bomb cannot accelerate and get extra damage from velocity. On the other hand, if you are dropping them on a planet from orbit gravity will do the work for you, or if the launching ship is already moving quickly relative to its target.
In the case of nukes I don't know how much larger you would be able to make the warhead. If it was a gun type nuke (propels a slug into the fissile mass inside the warhead) then the extra length might be handy. In the case of X-ray laser rods, a long cylinder would be able to carry more bundles of long, thin rods and would be a more suitable shape than a sphere.