If you are talking about the passages in the books that correspond to the C/P section, then it actually a very good indicator. That is, as long as you are averaging scores across the full spectrum of general chemistry, organic chemistry, physics, and the two metabolism chapters in the biology books. That's 32 sections total, and you should expect that your average score on those sections will be +/= 1 of your score on the C/P section of the MCAT.
While I appreciate where Kevin is coming from with respect to FLs, and I tend to agree with that statement for the most part, the phases in the books associated with C/P are the exception to that comment. They are scaled based on people's MCAT scores over the years. They are pretty good in terms of N value and they are based on over 4000 questions (the total number of questions in those sections.).
Are you by any chance doing the Zoom class with the books? The question sets with those are also a good indicator.