Perceived difficulty on the practice tests for the most part tends to be highly subjective depending on what content and style of questions you are familiar with. For everyone that says a certain practice test is difficult, there is another person who would disagree. In terms of closeness to the current test, the later ones - 10 and 11 - tend to be the most accurate. I would consider what other factors may have been at play here - alertness, level of burnout, distraction, content issues, critical thinking, etc.