John,
I agree that Marcus Green's Exams are the gold standard for predicting your performance on the real exam. In contrast, the score that you get on my exam will not correlate in any way to the real exam for at least two reasons. First, my exam does not yet cover all of the material. Second, the feedback that I have received (including your email) suggests that my questions are very difficult.
The value of my exam web site is the topic specific exams that can be used as a study tool as you work through any study guide chapter-by-chapter. For example, after reading a chapter that covers inheritance, then take my mock exam on that particular topic. Your score will probably be low, but you can learn from reading the explanations of each answer and by using the links to reference materials and by posting questions here.
It appears that you had already completed the study process and then you used my exam to measure your level of preparedness for the real exam. I will be the first to confess that I would have also scored poorly on my exam if I had done the same. I know that to be true because that is basically the point in time when I started developing the
test programs that are now the questions for my exam. I had already completed one of the study guides and I was scoring well on mock exams that I found on the web, but I realized that I was still having some problems with some of the concepts. I then started reading the JLS and then I wrote some test programs to confirm what I had learned. I was often surprised by the results. After I had a large collection of those programs, I decided to make them available on the web as a mock exam. Although I believe that my exam is a very good study tool, it should not be used to measure your level of preparedness for the real exam.