Formation experience leads to players to choose just one or 2 tactics at the beginning of the season and stick to it. And that happens all seasons, as the formation experience resets every season. 

My proposal includes two aspects of the formation experience: reset and max experience. 

The maximum experience

In order to allow for more rotation of formations, the maximum should be reduced to 3 stars or even 2 stars.

The reset

At the reset, the formation experience should be partially reset, not completely. Either it's reset in a fixed amount, for each non played day (with a cap of 2 or 3), or a mix of both. One way to do it is to drop the experience of the 5 oldest games at the reset, plus 2 games per non played day on that off season. 

This way, one could keep the formation of the last season, but not completely, with the drawback of not being able to start the season with a new formation, of course.

I have this idea:
Tactical experience for each player. (average of the last 10 games).
11 players will create the average experience of the whole team on the field.
No need to reset at the end of the season.