I almost always book for 2 and don't modify it. Rarely, if ever, is there actually a one top table so if you were to actually get it modified to one, you are going to be sat at a two top. They don't charge ever except for on pre-paid meals if less show up, as long as someone does. Usually when I check in, I just check in for one. No explanation and they don't need one (or frankly probably don't want one).