I think a lot of people on these forums credit the AI with far more intelligence than it actually has. There is no way that the computer is going to perform an in-depth analysis of the tactics you have used over the course of a season.
Your reputation plays a large part in the way opponents line up against you. This means that if you are thought of as relegation candidates, computer teams tend play against you in an attacking way even if you are actually way up the table. By the second season, your reputation has gone up, and your opponents will adjust tactics to suit.
Morale also plays a big part in your performance. In some older versions of Championship Manager, one defeat could destroy the self-confidence of your entire squad for several months. They seem to have toned it down a bit in more recent versions, but it is still a factor that can cause you to go on a run of poor form.