In wargames like this one, but also in Battletech and many other I know and play, the range of the weapons, and lack of LOS blocking, allows a lot of shooters to gang up on one target; this means that you can play a "shoot everything on one target, destroy it or at least cripple it, choose another, repeat until there are no more target".
This is in many case a winning tactic: while performance and firepower of one ship degrade with damage, it doesn't pay to split your fire, in the game or in reality. What makes splitting fire a good thing in reality are two other consideration:
1) if you completely ignore some targets, they are free to shoot you at leasure and more precisely; this is truer of ground battles, but apply also to other types of conflict.
2) this is VERY TRUE of naval warfare up until radar controlled fire: if someone other than you shoots at your target, you can't correct range and bearing with your "splashes", because you can't see which are your shoots and which are not (I immagine that in Leviathans, cannons use time fuses on the ordinance, to see where they go in case of misses).
In Leviathan, the (1) consideration can't be easily simulated, because you chose your target one ship at a time but we could give a d4 bonus (I haven't got the colour codes here) to ships not shot at the previous turn when they shoot this turn.
the (2) consideration is easier: the second shooter at the same target, downgrade his lesser dice by one grade (ex. d6 to d4; if you downgrade a d4, you lose it). The third shooter 2 downgrades, and so on.
What do you think?
Shard