I have to replace the toilet in one of my bathrooms. I understand that one needs to find the "rough in" size (10, 12 or 14) did that. read that to do that one measures from the wall to the center of thefloor bolt. got it. 13.5. means 14 which means special order. here is my question, asked of me by my BF, that i can't find the answer to. Why does it have to be a 14? why can one not just use a 12 and center it over the hole?