Using 2-cc coupler measures, MPO values for different programmed settings were compared for the premier hearing aid products from six major manufacturers. Large differences were observed, and these differences were not directly associated with the product’s OSPL90. In general, at least for the sample audiogram used, it appears that the MPO is limited by the gain setting and the aggressiveness of the wide dynamic range compression (WDRC), often restricting useable headroom.