it's not quite correct.
"B=" is a electric bus number to which the display is "connected". It is not relevant now, since we are changing the whole electric power configuration.
"b=" is NOT a brightness value! This is a number of "brightness channel" in your virtual cockpit, that you want to use for this display. Then, you can rotate related brightness knob in your virtual panel to change the brts.
So, the b can be 0,1,2,... sometimes it can be any other number, depending on your plane model configuration.
If the plane has channel number for it's AP as 25, so use it.
And - we will change the brightness control in the configurator, it will be "device-oriented" and use the pre-defined SImVim BRT names.