A few reasons they rear fire:
-Front baffle is too small to fit port. (I think this applies to the R200DB and S1000)
-Port is large and midrange is audible through the port. (Internal foam lining can take care most of the problem)
-Undersized port (so they can make it short enough to fit) so there's chuffing.
-Purposely done for bass reinforcement by rear wall.

I've done experiments on my own with a 5-inch and 2-inch. With the smaller 2-inch driver it's difficult to pin-point. With the larger 5-inch though with a 2-inch and 8.5cm ports, I prefer that to be facing away from me in both cases.

This is only applicable for nearfield. I built an MLTL tower with the 5-inch, had the port at the bottom (naturally) and facing back. Now I am building a pair that is shorter but deeper, with a much smaller port, and forward firing. Because of the foam lining and stuffing in them, other frequencies are whisper quiet and muffled in both cases (even more so in this new one). So the rear firing port is impractical and unnecessary in this case.

Front firing ports are FAR more practical though since you don't have to worry about it being too close to the back wall.

This post has been edited by VagueConcerns: Oct 23 2015, 03:38 PM