I'm not sure that the inlet length has anything to do with icing, as the phenomenon occurs at the venturis, but it might put the carbs a long way from the engine heat, so allowing it to happen more readily?
Moisture is sucked out of the air when it is accelerated and the pressure drops dramatically, as in the venturi and also on the lifting surface of a wing at high speed and G.
That's a pretty graphic description of what's going on inside your carb.
There is also a temperature drop which can cause the vapour to freeze, as in con trails and carburettors. You have the goldilocks conditions for it @ 2 degrees and 100% humidity.
I think it's unlikely to have anything to do with the petrol except that it will rob further heat from the environment when trying to turn from a mist to a vapour.
I'm no scientist and can't see how a fuel additive works when the phenomenon is in the air/moisture part of the mixture.
I think it's better to treat the incoming air in some way. In the olden days of carburated cars, there was always a summer/winter position for the intake, with Winter being directly over the hot exhaust. That's tricky on a Monster though! Not much room under the tank to duct air from somewhere warmer?
Stopping the engine for a few seconds allows the heat to migrate into the carbs and thaw them out, sometimes it comes to the point when the ice stops it anyway!
I once stopped to help a stranded motorcyclist with a frozen carb. (I think it was a C15?) I suggested weeing on it would soon thaw it out. The poor rider just indicated their inability to do so all togged up against the cold, so I happily obliged and blow me it started and ran.
I got a lovely thank you letter from a Miss Carol McTavish.