There are two things that greatly affect the M2’s response, strapping and calibration. The strapping should be carefully adjusted so you can feel all the frequencies, have contact in all working positions, and feel comfortable. You will need to spend time initially listening to the calibration track, reference tones and material to adjust the strapping system to your body. Find the right balance of pressure and contact first.
Notice that the top and the bottom of the unit need to be in contact with your body for full frequency response. Adjust the straps to achieve various vertical positions for maximum contact. Pressure between the unit and your body can aid in this contact, but too much will impede the transducers. Stop adjusting when you find a balance between comfort, contact, pressure and a smooth response.