Collocated active vibration control is an effective and robustly stable way of adding damping to the performance limiting vibrations of a plant. Besides the physical parameters of the Active Damping Unit (ADU) containing the collocated actuator and sensor, its location with respect to the compliances in the plant plays an important role in the performance of the active vibration controller (AVC). This paper presents a model based evaluation of the interaction between the AVC and the plant, for two variants of the ADU location in the plant. It is concluded that the ADU should be placed as close as possible to the end effector to achieve optimal damping and exclude the excitation of undesired dynamics by the AVC.