"...if the defender is in a fleet, they do get some bonuses, reflecting the support the other ships can provide."
How is this bonus calculated? It seems to cause all sorts of weird results. The AI is constantly throwing away frigates against my stacked corvettes. The bonuses don't seem to apply when the fleet is defending a planet.
The fleet defense bonus is buggy. Cari said that there is a logical error causing the attacker to be destroyed and that this bonus has been removed for the latest beta builds.
Stacked Starfighters can take out Overlords under 1.05 so it's obvious that something is wrong.
The stacking bonus does not work with ships in planets.