TimeQuest Timing Analyzer[Setup slack analysis]

You're correct that in a traditional sense, the uTsu is subtracted from the Data Arrival Time, making the slack worse(or making it harder to meet timing). I have submitted cases like this for analysis, and it comes back that it's the way it's modeled. In essence, the data path at the register might be longer than it should be, and the uTsu becomes negative to account for that. In essence, it was determined to be correct, but I get what you're saying and it is confusing.