Nashbar steel frame owners
 

I'm looking to pick up one and have read many of the threads regarding them but I have a question about their sizing. I normally ride a 23 in. top tube length, which usually falls around a 19 to 20 in. frame size for most manufacturers, but for the Nashbar frame I would need their 23 in. The 23 in. has an overal seat tube length of about 20 in. which seems more like the 19 to 20 in. frame size. Is the Nashbar sizing just different from the others? It just seems strange that they call this a 23 in. frame size. Thanks.