What percentage of people with alien implants from abductions have an alien portal in their home or workplace?

At least one third of alien abductees also have a permanent portal installed on the premises, the point from which it is mutually most convenient to gain access to the human's environment and extract them for study or other purposes. This creates a greater level of security for the clandestine manipulation that is less demanding with regard to overriding the observations of a large group of potential witnesses in many settings, as the intrusion can be carried out via interdimensional transport without the need for a nearby craft that must hover and allow potential observation of the comings and goings directly by unexpected witnesses. So this is part of the broad-scale effort and a routine element.