Relative strength of of yours and your opponent team is one constant. That doesn't change. What influence the final outfit of the game is more complex and I guess only handful of people actually know the full story about it. Rest of us can only guess. Different tactics do different things, they fit players in different ways and they counter your opponent tactic in different way as well. Small things like saying something in press conference can affect how both yours and your opponent team will play.Forgot to mention my concern about it. If I play 30 times, I'm trying out different things that's why I'm playing it 30 times. As an example I use the same tactics for 5 games, leave it to the assistant for the next 5, then a different tactic and so on. That's the thing I don't get. It only took one game to see a massive difference in the gameplay vs Birmingham, then again I could go on with reloading for an hour in another game.
I'm still not sure whats your concern. Is it that results are too similar when you try different things or vice versa?