How big should center spkr be to set to "large"?

I have actually tried both small and large settings for my current setup. I have no problems with clarity or bass response with the center speaker set to large. All of my speakers are set to large and i don't use a sub. I have also used a test disc with a sound pressure meter and the 570 will do 25Hz easily in my room.(Can do 20Hz but not too audible mind you, but it will do it.)
Could be as simple as different equipment,different results.

"Could part of the problem be putting the center channel on top of the RPTV?"

Yes a little, but the main problem is a dramatic spectal balance mismatch between the main speakers and the center, further aggravated by there being no sub. Which I realize he cannot buy, and that's ok just swap the 570 for a Silver Screen should be a wash financially.

Also CDW with a sub in the system, many receivers will allow you to set the crossover at 40-60-160hz and the range can be covered at 1dB to 10dB intervals. A center like the 570 I would crossover somewhere between 50 and 60 hz.

I played around with it some more tonight, watching 5.1 movies and a Black Crows concert on HD cable.

Actually, tonight I could hear no ill effect from setting the center speaker to "large". It did't seem to cause any loss of clarity in the center speaker, nor did it seem to cause any loss of overall bass. I really liked the overall sound with that setting.

I am going to try it on some DVDs and HD DVDs as well.

Mtrot, How is your setup working out?

Actually, I am now quite pleased with the system, both on movies and music. Last night, I toggled the center speaker between "small" and "large", and I think it really sounded a bit better overall with it set to "large". I am going to leave it set that way for a while.

I now think some of the problems I alluded to in my original post about setting the center speaker to "large" must stem from my recollections from when I was using my Panny RP-91's onboard decoder. Now that I am decoding with my Sony DA4ES, setting the center to "large" is sounding real good. I don't run real high volume levels, so that may be why I don't seem to be having problems with overdriving the Paradigm, and thereby getting distortion.