set speakers large or small?

Your main speakers roll off at around 50hz, if you set them to large just where you gonna make up those missing 30hz?.....thats a huge gap in sound. You set all to small, roll off mains at 60, center at 60 rears at 80hz and set your sub to cut off at 80hz.........thats the proper way to do it. Why would anyone tell a speaker that rolls off that high that it is "large"?

If your speakers and amps can handle a lower setting than 80hz then ignore THX cause you gonna enjoy it more if you do. THX was invented and its more about consumer speaker size than anything else.