A method comprising: establishing a transducer array having a plurality of ultrasonic transducers with known relative positions and orientations; defining a control field having a known spatial relationship relative to the transducer array; defining a point of interest in the control field; defining a direction of energy flux at the point of interest as a wave vector; calculating an acoustic pressure profile within the control field using a plane normal to the wave vector; characterized by defining a desired spatial size of an acoustic region around the point of interest in the plane normal to the wave vector; estimating a relationship between the desired spatial size of the acoustic region at the point of interest and a focus location along a first line defined by a geometric center of the transducer array and proceeding into the control field along the wave vector; determining the focus location using the relationship that provides the desired spatial size of the acoustic region around the point of interest ; driving the ultrasonic transducers to create a focus at the focus location ; wherein the estimate of the relationship between the spatial size of the acoustic region at the point of interest and the focus location along the first line defined by the geometric center of the array includes generating a volume by determining a distance between a focus point of the control field and the geometric center of the transducer array using an imaginary boundary through an edge of the transducer array converging through the focus point; wherein the focus location is offset from the point of interest . establishing a transducer array having a plurality of ultrasonic transducers with known relative positions and orientations; defining a control field having a known spatial relationship relative to the transducer array; defining a point of interest in the control field; defining a direction of energy flux at the point of interest as a wave vector; calculating an acoustic pressure profile within the control field using a plane normal to the wave vector; characterized by defining a desired spatial size of an acoustic region around the point of interest in the plane normal to the wave vector; estimating a relationship between the desired spatial size of the acoustic region at the point of interest and a focus location along a first line defined by a geometric center of the transducer array and proceeding into the control field along the wave vector; determining the focus location using the relationship that provides the desired spatial size of the acoustic region around the point of interest ; driving the ultrasonic transducers to create a focus at the focus location ; wherein the estimate of the relationship between the spatial size of the acoustic region at the point of interest and the focus location along the first line defined by the geometric center of the array includes generating a volume by determining a distance between a focus point of the control field and the geometric center of the transducer array using an imaginary boundary through an edge of the transducer array converging through the focus point; wherein the focus location is offset from the point of interest . <EOS>