As I understand it the FBS machines do not like air between the coil and undisturbed soil matrix. They supposedly do not do well in plowed, fluffed fields. Some of my hunting sites are in pine forests. My question is; Would the fluffy pine straw mat above the soil cause the FBS detectors to suffer loss of depth due to the air filled pockets in say a 3in. or so mat of pine straw? Would a single frequency detector penetrate this environment better? Any thoughts?