Not sure if I quite understand what you are asking but hope the following helps:
Playing TIE will increase enthusiasm by 33%.
Playing Normal will not affect enthusiasm level.
Playing CT will decrease enthusiasm by 50%.
Also enthusiasm tends back to 5 each day.
For example if your enthusiasm is 12, then the next day it might be 9, then a few days later it might be 8, then a week later it might be 7. Make sense? As you get closer to 5, the enthusiasm takes longer to get back to 5.