For the VCF Mode control of Dark Energy II and III a different potentiometer type is used. This is equipped with an additional center tap to obtain the continuous filter mode transitions.

The manufacturer is not able to offer this type of potentiometer with the thread that is used to fix all other potentiometers to the front panel. That's why the VCF Mode control is not fixed to the front panel.

On the Dark Energy II information page this particularity of the VCF mode control is expressly mentioned !