All the models in the POD are optimized for the best possible combination of gain, headroom, and signal to noise (s/n) ratio. Since the different amps can have very different gain characteristics, a setting of 6 on the Channel Volume knob isn’t necessarily the same
absolute volume on any two given models. When you change to a new amp model from the Model Select knob, it automatically loads an optimized Channel Volume setting (this setting is different for each model) so that, as you step through all the models, they are all about
the same level. If you’ve cranked the Channel Volume on a particular patch and then change the model, it just loads the default setting as a starting point.