Cattivo,
The system is extremely fair and the performace in the simulator is directly compared to your relative experience as passed to BA with your application and then assessed. You will not get a pass/fail at the end of the simulator. Someone with a large amount of experience will therefore be assessed in a similar manner to someone who has relatively little.
As I said above the check is to determine your approach to problem solving and your ability to pass successfully the BA type rating course. Just apply a logical approach to problem solving, try and involve your sim partner in the decision making and, if a definitive answer needs to be made, don't provaricate and make a decision. If what you get back from your sim partner doesn't fit your mental model then explain why and explain what your decision is. The ability to include ATC, Cabin Crew, Commercial expediency and the passengers in your process is a big bonus that generally tend to show capacity, just don't crash the jumbo whilst doing it!
The assessment is relative to each individual so don't feel under pressure from some sky god in the other seat just give YOUR best!
Edited to add: Your assessment, comparitive to your experience, will be judged against your peer group. To be honest I dont think there is any other way for a fair system.