I have to say Gene, that I have posted with just these views for years now.
The center does end up to be a problem with TV screens. You have placement issues plus aesthetics. The you have the space power problem. The just as important what is the optimal radiation pattern?
I agree that the most common horizontal MTM arrangement does leave you with a very compromised system. The radiation pattern is the opposite of everything desired.
One aspect you did not get into, was the interaction of the front three. In most domestic situations the speakers end up too close together. This can and does lead to interference between the speakers. In addition the reflections from the screen are a potential problem.
If aesthetics permit, I agree that the center is best above the screen, but this does leave the speaker too high. However I agree, better too high than too low. The height does have the advantage of broadcasting the dialog over the whole theater.
In my case having identical three front speakers would have been impractical. However my researches showed three identical speakers not to be the optimal solution.
In my view a coaxial or a good full ranger (the latter is a problem) is the best solution. This allows a radiation pattern covering the listening area and minimized speaker interference. The single sound source can be placed very close to the screen and the solution absolutely keeps voices locked to the screen.
So I deigned this little though wall center TL for the SEAS coaxial drivers.
It is installed to face the listening area.
This is the finished result.
The lower driver is crossed at 2.8 KHz and the upper driver carries BSC actively. With the protrusion from the wall BSC is required and those drivers seem to have an roll off in addition below 500 Hz. I did eventually create a network, that was far too much work to flatten the response irregularity in the 9 KHz region and flatten the response to 20 KHz. This utilizes the tweeter in the upper driver. If you put your ear to this tweeter you don't hear a lot from it, but the improvement is subtle and worthwhile and aids speech intelligibility.
The front sound stage is very stable and if you play all three mono they sound identical as you move across. I watch a lot of operas and they are no changes in the quality or the timbre of the voices as they move about the stage.
I have been very pleased with this center speaker. It has really good vocal quality that is uniform over the listening area for voice spoken and sung.
Now the system at our other residence that also contains a center speaker.
Now this is a Condo with a couple of shared walls, so I have to be careful.
Now this is a difficult room as the fireplace is opposite the screen. This makes for an unusual seating arrangement.
Initially I just installed a rudimentary system here. However my wife was adamant that something better was required.
Since the seats are at the margins of the right and left speakers a center would be desirable.
The main speaker look line 2.5 ways, but they actually are 3.5 ways, as there a couple of Morel 9" sub drivers in each cabinet.
The tweeters a Scanspeak crossed in at 3 KHz and the mid/bass drivers are Dynaudio high power extended range drivers. Each is in its own sealed enclosure. Extension is to 90 Hz. The bass units are coupled cavity isobarik, with one sealed and one ported compartment. 3db points are 27 Hz and 90 Hz. For this bandwidth I had to settle for a Q of 0.7. This obviously won't knock the house down, but in the confines of this condo the bass is more than adequate.
So what to do about the center? There is not much space, so I used one of my 4" Jordan Watts aluminum full range drivers. In that box, response extends to 90 Hz where there are crossed over. This little drivers have a very smooth extended response with zero peaked sudden break up modes. They are bend by design, and the cone is basically a tractrix piece of foil. The radiating area decreases linearly as frequency increases.
The result is excellent with clear dialog locked to the screen and another excellent blend with the mains!
I sent one of these drivers to fuzz and he built a sealed enclosure to my spec and was astonished as was Walter Dubuque who heard it there. I have never known anyone not astonished by these little drivers.
These appeared in 1959 and have proved that excellent wide band drivers are possible. Unfortunately most have ignored that fact.
Power is Quad 909 to the left and right top ends, a Quad 405 II on the bass section and one channel of a Quad 405 II on the center.
Then there is the possibility of no center.
In this confined area the lack is center is no problem. This is mainly a music system.
Speakers are three way, with two external subs.
Crossovers 400 Hz and 4 KHz. The excellent Dynaudio D76 covers the whole speech discrimination and speech is excellent.
In my view the advent of HT has made us up our game in many ways. I have included a TV in the mix since the invention of the VHS recorder.
In my view a speaker that can not reproduce natural speech is a lousy speaker period. Too many speakers fail right on this issue.