Well, you do have to get the water bath temperature right to get the chemistry to the correct temperature. My CPP-2 (early model) seems to need about 0.5C higher setting to get the process temperature correct. I use both a Kodak process thermometer and an electronic one (both agree with each other). I determined that setting using water in the bottles and when all was figured out, I mixed, heated up and processed. I usually start the CPP heating 2-3 hours before I run it. After loading the film, I pre-heat the drum (rolling) for 10 minutes or so depending on the ambient. Great results.
Of course, correct exposure in the camera plays a big part in success.