What i am trying to say is that the frames were designed to have long top tubes, slack HA and a steep ST. By sizing ‘down’ you are in effect negating the original design intention of the long TT, so if you would normally ride an 18″ ST, with say a 23″ TT i would stick with the seat tube size rather than pick by TT length as most would normally do, if that makes sense?
Not that it really matters, pick what works for you, im just rambling 🙂