yes it's a display bug. Same logic as for the XPDR applies, you should read WX/T , TURB , MAP.
You need to make your own SIOC script.
First create a dummy pot in SIOC Creator for the gain (ie assign a fake input number which is not used in your system).
Then add you own script which will change the value of that variable based on your switches linked to your own script.
The values are from 0 to 255 if I remember well here, 0 being the minimum 128 middle and 255 maximum.
regards