When you click Manage for a fleet, a panel pops up that lets you add ships that are at the same location. If there's a ship selected you'll see its current attributes (base plus starbase bonuses plus fleet bonuses) at the bottom of the panel. However this part doesn't function properly if there's a ship with a fleet defence module. Instead of merely adding on the bonus for that one ship, the entire fleet's bonus is added in the one ship's info display. I think though that this is cosmetic and the actual defence in combat is calculated correctly, 'cause otherwise I would never lose a battle.