[Fyron]

Strength is irrelevant. Evil Duckie was close. Construction order (possibly that ship ID number thing, which might obfuscate the exact ordering after some ships have been destroyed...) is what determines the order the ships are placed in the slots of the fleet. The leader is the ship you designate as the leader, but all other positions are out of your control. The order you add ships to the fleet is also irrelevant (other than determining the leader when you first create the fleet; the first ship added is the leader for a newly created fleet).

Ships without weapons are not placed in the formation. They are scattered randomly around the battlefield (as are extra warships that do not fit in the formation when you have too many), generally behind the fleet, but not always. This random placement is the same method used for a group of unfleeted warships (such as when you have a group of ships orbiting a world and you are attacked). It is a very poor solution, but it is what the game does.