What is the deal with Becos FX’ recessed DC Power Connector which require a DC Power Plug with a 12mm long barrel?

We use common DC Power Connectors that are soldered directly on the circuit board, recessed behind the 2mm thick enclosure wall. A DC Power Plug with a 12mm long barrel having Ø5.1mm external diameter and Ø2.1mm inner diameter is needed for a good electrical connection inside the connector.