Various systems and methods for controlling an ultrasonic surgical instrument according to the location of tissue grasped within an end effector are disclosed. A control circuit can be configured to apply varying power levels, via a generator, to an ultrasonic transducer driving an ultrasonic electromechanical system to oscillate an ultrasonic blade. Further, the control circuit can measure impedances of the ultrasonic transducer corresponding to the varying power levels and determine a location of tissue positioned within the end effector according to a difference between the impedances of the ultrasonic transducer relative to a threshold.