ClarkPeters correctly identified the problem with the nonadjustable nature of the horse-collar pad. For most people, the horse-collar will be too close to the neck and exert downward pressure on the trapezius muscles, which will in turn exert pressure on the neck vertebrae causing neck pain when used for an extended period of time. Adjustable yoke pads can be moved toward the end of the trapezius muscles and avoid having the muscles pull downward on the neck:
If you raise your left arm over your head, then use your right hand to feel the flat spot between the trapezius and the deltoid muscles, that is the spot where the portage pad should land.