Isn't it better to send several smaller fleets with a lower chance of success? From the single planet I've taken it seemed every fleet got a chance for capitulation each turn so my mass of 5% chances took the planet in 3 days or so.
That has been my tactic as well, you can get a much better aggregate chance by spending your resources on smaller fleets then on bigger ones. Of course if you are fighting an active player, which few of us seem to do then the small fleet tactic has its draw backs.
