I believe the acceptable losses are set for everyone. i.e. This season's reported finances 8m is acceptable, for next season it is 5m, regardless of how much was lost last season.
It depends on how it is weighted. The Opta statistics cover time on the ball, passes attempted, pass accuracy, range of passes, areas covered, etc. You can change the trigger points for different players to suit their game and what you expect from them. A 95% pass accuracy on 50+ passes per...
I seem to remember reading recently (like over the summer) that relegation clauses were starting to be used a bit more now (though still not yet common place) that previously the PFA had been against them. Perhaps it depends on the player and how desperate they are to play in the premier league...