Not trying to throw fuel on the decoction debate fire, but I've got a question:
What temperature does the decoction boil at?
I realize that "212 degrees at sea level on a standard day" would be the default answer...but doesn't the presence of sugars perhaps raise that temperature? Consider candy making: as more water is boiled away from the sugar solution, the temperature increases. Granted, that is a MUCH thicker sugar solution than you'd likely find in a decoction boil, but the temperature should in theory still be higher.