Dog... the 3 sec carb heat on the ground will tell you nothing use it untill you are sure that no ice is presant IE that after the inital RPM drop there is no rise after about 10 sec then there is no ice.
As for carb heat and full power i to have been told of detonation problems (is this another myth) but have yet to see eny evidence of this when i have removed cylinders i think that it MAY be a problem if the OAT is very hot,max power is my only reason for insisting that the carb heat is not used on the GA.