[Jmenschenfresser]

I think fleets matter alot in combat results. It's been my experience that you need to put ships in fleets and set the strategies to what you have in the actual game.

Sounds like at least the mistake went your way. I had one where I destroyed all my opponents ships in the sim losing around 30% myself. But when the actual battle came, I lost all of mine and he lost one or two. Complete reversal.