Here is the situation. I move a fleet of 5 ships into orbit and notice that there are 4 ships defending. When i initiate battle, it's my FLEET vs 1 ship. Then i easily win the battle and i can repeat this until all 4 ships are dead. Now, i take no losses with minor damage if at all. If the ships around a planet acted as a fleet, then i would take much more damage and perhaps even lose to 4 better armed ships that i can just pick off when they fight solo.
The downside of "fixing" this, though it might be worth a fix, is that a planet can be defended by many ships(10 maybe?) and you can't invade to the planet until all the ships are out of the orbit. So it would seem to me you could protect your planet at least for a few turns by keeping a full orbit of ships. Now some might cheese and quickly build 10 unarmed hulls(satilites) just so they can kick them out in 1turn.
Just thought it might improve things to combine into one fleet on the planet.
Brian