Let me preface this with the basic understanding that sound reproduction is an integral combination of speaker/room/listener. However, is there a significant difference in the sensitivity of how rear vs. front ported speakers (especially 'bookshelf' speakers) utilize the wall behind them to project the sound? I have a room configured like a classic art studio with a large open central space, but with the walls plugged with shelves, cabinets, equipment hanging, etc. all the way dow to the floor. There really isn't much clean unobscructed wall space...if a rear ported needs a clean wall to bounce the sound off of, in here it will tumble into obstructions and a labyrinth instead. I've read about the need to pull a rear ported speaker out from the wall...but does it really need an unobstructed space behind it?
The frequencies that come from the area of the port are bass frequencies. Unless the port is rather poorly designed (ports are not that selective and midrange frequencies can escape the enclosure also), anything that low in frequency is omni directional in nature. The placement of the enclosure relative to the wall is an attempt to maximize the in phase reflections from the front mounted woofer and the rear mounted port. Depending on the frequencies the two devices are working with, some frequencies will add and reinforce (in phase) and most everything else will cancel and subtract (out of phase). Everything in between those two extremes will be some where in the middle of additive and subtractive and can result in muddy bass/mid bass response. This is the nature of a ported speaker. By utilizing placement, you are trying to maximize the reflections from a rear ported speaker to place the most in phase information at your ears across the room.
The description you give would indicate a rather diffuse rear wall pattern. This should make placement somewhat easier but will probably give a bit less bass reinforcement than a solid wall with a smooth corner. Of the two, I would opt for your situation over the boominess corner placement will give most speakers.
"The placement of the enclosure relative to the wall is an attempt to maximize the in phase reflections from the front mounted woofer and the rear mounted port."
This probably confusing even thoug I knew exactly what I meant when I typed it. Try this instead:
"The placement of the enclosure relative to the wall is an attempt to maximize the backwave signals coming from the rear mounted port by maintaining their in phase relationship with the signals from the front mounted woofer."