The satellite count is based on the satellites being used in the solution. With Fix or even Float, the engines will use all signals that are being tracked and that are in the correction stream. If the correction stream drops a constellation, the satellite count will reflect that. CDF which stands for Code Float, is usually using SBAS (Space-Based Augmentation System) data, such as the FAA's WAAS system over North America. WAAS only provides corrections for GPS, so this is why you may be tracking 30 satellites, but then get a CDF solution and the count drops to 10, because you are only tracking, for example 10 GPS satellites. STN which is a Stand-Alone Solution (or autonomous), uses all signals being tracked, so you might even see your count go up if the corrections you're using are, for example, GPS and Glonass only, while the LS is set to track GPS, Glonass, Galileo, and Beidou.