I am much more familiar with offroad geometry than road/gravel geometry. I am building myself a gravel road bike with offroad drop bars. I have a great fit on my MTB, so how much shorter would the recommendation be for the TT length compared to the 3/4" riser setup I currently use to get a similar riding position? I don't need perfect, just a starting point,as this is a practice frame, and I can adjust as needed as I get closer to my best fit through my next few practice frames. I read 6cm in another thread, is this about right?