dont see why he would say that... its just a calulator with the same formula every other program on earth uses. If you really wanted to you could use WinISD and get the T/S specs off kickers sight to enter your own sub. But I say go for what you said. So long as you are entering the right information in that web page its close enough. But if 5.29 already takes into account the port displacement and woofer displacement then you should be fine.