I had to work a bit on the best position of the transducer--so I do believe that it is related to being just below the hull by about 1/8" (I had it flush at first). I don't do Radar overlay. I wonder what heading sensor you would use for the overlay? Generally the delay on the GPS is too long--the best heading sensor is a gyro fluxgate compass. I would check the manual (mine does not support radar). I use Furuno Radar, with separate screen.