Mir's forward and rear docking ports are used to receive all incoming vehicles. Side ports can only be used by moving modules to and fro on a small manipulator arm.
Before the first NASA shuttle docking, the Spektr module docked to Mir and required rearranging the position of the Kristall module as shown below.
Below - Kristall to moved to a side port to make way to Spectr
Above - Other Kristall solar array is retracted to clear the docking area
Below - Spectr Docks
Above - Spectr is moved to a side port
Below - Kristall is moved back to froward port for STS-71 docking
Above - Kristall returns to side port to clear forward port
