The saddle rail clamps are behind the axis of the seat post. This one is pretty extreme in that regard, letting me use a saddle with shorter rails, typical of leather saddles such Brooks, Gilles Berthoud and this Rivet, in my preferred position for my long femurs.

I’ve had the 1979 bike shown for its entire 41-year life, and this seatpost has resulted in my most comfortable fit, feeling like I’m riding “in the bike”, not on it. Saddles with longer rails reduce the need for setback, but I’ve also learned that my posterior asymmetry requires leather saddles like this for rides longer than 30 miles. I had a Selle Anatomica, which is also leather and with quite long rails, on a shorter setback seatpost for the same fit, but other aspects about that brand’s shape didn’t agree with me.

The need for setback is reduced for a given saddle position relative to the bottom bracket as seat tube angle is relaxed.