It's ideal for it to be set with a crossover setting and to be set to small if you want better surround quality. If your speakers are not all large and the instructions don't say to use the large setting than a center channel set to large (meaning it will use full range) can rob sound (frequencies,Watts,perception) from your other speakers.
I'm pretty sure thats recommended by THX when using a DTS setting but they just do that to make up for lost treable I think.
Otherwise I have always heard that it's not supposed to be full range.
You can read what they think here.If you can find it. I couldn't. http://www.thx.com
It all depends what type of speaker you have mostly.