A distinct characteristic in Acoustic Gallery Scanning Probe Microscopy (AG-SPM) constitutes the use of its supporting structural frame as an acoustic resonant cavity for monitoring the nanometer-sized amplitude of its stylus-probe. Although very straightforward in its implementation, its amplitude detection sensitivity could be improved by a more thorough understanding of its working principle mechanism, as well as by a more systematic procedure to attain a closer matching between one of the cavitys acoustic resonances and the probes natural frequency. Herein, a description of the working principle of the AG-SPM is attempted from a vibrationalmode analysis perspective, and a successful specific procedure is presented to maximize the AG acoustic response. Such an improvement in sensitivity will make AG-SPM a better metrology instrumentation to study probe-sample shear-force interactions at nanometer scale separation distances, as well as its role in the fabrication of nanostructures via SPM.