Installed fiberglass performs at a much lower R-value than the fiberglass companies advertise. Oak Ridge National Laboratories tested wall structures 
insulated with fiberglass and found that normally installed fiberglass loses 28% of its advertised R-value.
R-value does not account for air movement within structures.
Foam will perform the same both in the laboratory and in the field because it glues itself in place, does not settle or sag over time, and does not allow air to travel through itself.