that would create a kind of distortion:
for someone sitting in front of the RF speaker, sounds from the LF speaker would move over towards the RF speaker, but the sound from the CF would not move as much as the rest.
is my thinking right?
How the sound moves relative to speaker/listening position will depend on how itís mixed. Not all sound coming from the mains is the same. A door closing off stage left is still going to come from the left speaker no matter where you sit if it was mixed that way. Anything that is mixed evenly between the two mains, often drummers and lead singers in bands and much movie dialogue will move closer to the nearest main speaker. How great this effect is depends on how far apart your speakers are, how off center you sit and how far from the screen you sit. In your case you canít get very far off center, your mains arenít very far apart both of which will help to keep the front soundstage imaged around the screen.
Sitting very close can make the sound seem more like itís coming from the speaker itself rather than a generalized soundfield centered around the screen. However, this also holds true for a center speaker where if you sit very close the center, since it often has less blending with the mains, than they have with each other, can sound like a point source. So you end up hearing the speaker as distinct and separate from the rest of the sound field. This is most likely to happen with a vertical speaker. On the other hand if you have a horizontal center and sit very close it can blur the imaging especially of a stereo recording being played back in multi-channel. This can also happen with things like movie dialogue where it should sound like itís coming from a particular character on each side of the screen but instead gets all blended together by a horizontal center.
To give you a perspective I have 3 M80s as L/C/R. I often turn off my center M80 when listening to well mastered music where I want the surround speakers engaged but donít want the issues a center can cause for a well mastered front soundstage. I also often have to tweak things when watching things on Netflix, which I only get in two channel, because the receiver in multi-channel pulls all the dialogue to the center while leaving the music and sound effects alone. With my mains over 12 feet apart what I end up with is much of the sound field collapsing to the center speaker. Instead I switch over to Dolby PLIIx and use the controls to adjust the width of the center image so it blends with the rest of the soundstage.
If you or anyone is interested Iím sure somewhere around here are the lengthy comments I made while testing center speakers in my apartment and house. Iíve tried a VP150, single M22s, double M22s (both vertical (each side of the screen and above and below the screen) and horizontal), single M2, a vertical upright M80 and a vertical upside-down M80 and phantom M80s. The results were so dependent on the situation, room, seating, speaker position, source material etc. . ., that the only generalization I can make is if you need/want a center speaker getting one identical to your mains, or as closely sonically matched, is almost always going to sound best, but even this isnít an absolute. So there just isnít any simple - things always sound better with a center speaker solution.