We have proposed a Multi-portal Human Interface (M-HI) as an innovative human interface for power assist systems (PAS). The M-HI allows users to apply the operational force anywhere on the power assist system. Because of that, the effective workspace of the PAS is extended as their end-effecter can be controlled as a user desires. However, when users control the PAS on its intermediate joint, the control point motion is different from the end-effecter motion. This motion affects maneuverability of the PAS. In this paper, we consider the number of links and degrees of freedom on a multi-link manipulator. The relation between the control point motion and maneuverability is analyzed. The operational point motion harmonization (OPMH) is based on this relation. This method enables users to control the PAS with M-HI more accurately.