Having the port on the back of a loudspeaker means that you theoretically have to have the loudspeaker at least a port diameter's width away from any flat surface. If you have a 3" diameter rear port then it should theoretically be at least 3" away from a back wall. I believe that the K2-S5800 uses two 2.75" diameter ports to tune a 4.5 cubic foot volume to 30 Hz. At one point it appears those flared ports are just 2" in diameter.The OM says these can be placed very close to the back wall, stating 2-3" is adequate, allowing enough room only for connections........ how is that possible as a rear ported design? why wouldn't standard coupling conventions apply here?
If rear ported loudspeakers have to be backed right up next to a wall for whatever reason then you are probably better off stuffing the ports and using a subwoofer.
One argument for rear porting is that it marginalizes any internal reflections exiting the port. Another argument is that it doesn't visually impact an otherwise perfectly finished baffle. It also decreases the relative efficiency of the port with respect to the drive unit.