Typical boundary reinforcement from placement close to the wall would be roughly +3 dB per octave. So I like to aim for roughly -3 dB per octave rolloff across the lower part of the bass region when the speakers are going close to the wall. I call this "room gain complementary" - or RGC - tuning. It's not quite the same thing as extended bass shelf - or EBS- tuning, but they are variations on the same theme. RGC tuning usually calls for a bit smaller box than EBS tuning. And as has been mentioned, port location doesn't really matter, though I personally think the argument can be made that rear porting offers a couple of potential small advantages when tuned properly.
Here's a more lengthy look at room gain complementary tuning, if anybody's interested:
http://www.audiocircle.com/index.php?topic=61810.msg890800#msg890800
Having a wall right behind the speaker will affect any midrange energy that wraps around the baffle and then bounces off the wall, introducing peaks and dips in the frequency response as the wall bounce energy goes in and out of phase, depending on the distance and wavelength. This can be minimized by blending the speaker into the wall as much as possible (perhaps via a very shallow enclosure), or by using drivers that are inherently strongly directional and/or using a wide baffle so that relatively little midrange energy wraps around the baffle and bounces off the wall.
Imo, ime, ymmv, etc.
Duke
dealer/manufacturer
