So...the front sight is part of the gas system then?
Yep. the gas tube takes gas from the barrel and directs it to the bolt.
The idea behind the dissapator is to use a carbine length barrel
with a rifle length gas system
. That way the gas is at a lower pressure when it is tapped off of the barrel as it is further from the chamber. The idea is that it doesn't cause the action to work as hard, that is, the gas impulse is not a strong as when it is tapped off closer. There is some evidence that there is less wear with this set up.