Have not had problems with carb icing in a C150 except on the ground with a relatively cold engine. No problems in the air.
Carb heat on for practice forced landings, all approaches and stalls. On approach, carb heat off at 300 feet. Temperatures down to about 10 C. Humidity not more than about 60 percent I think.
I don't know for sure, but I suspect the C150 has a relativley big engine which is strangled with a small carb to give 100 HP. This would mean that the pressure drop across the carb is going to be bigger (hence more icing potential) than for other engines.
Please feel free to correct me.