From "Damage per round" info:
"Attack per round is an average total damage made by unit during one round of a battle. Units have the ability to make concentrated damage. They can group to take down enemy units one by one instead of spreading their fire between all of them. If the enemy units group is the nearest one, about 50% of units will attack one specific target for destruction."
Anyone knows, how to switch a fleet into concentrated damage mode?

During the battle, click on the units whose fire you want to concentrate.  Then use the "attack" button and click on their target.  These units will concentrate their fire for the next 2 rounds (I think, but not entirely certain), or until the targeted units are destroyed - whichever comes first.  Of course, you can always repeat this (when you have action points) if they don't kill the targeted enemy in 2 rounds :)

Thank you :)