Two thoughts. One, a seatpost is best when the setback is such that the clamp is somewhere in the middle, not slammed. The ti railed seats I like for comfort tend to break sooner if I clamp the start of the bend and I like having a little more room to go on any adjustment. Slammed and no further possible always felt wrong to me, whether it be stems or seat rails. To me it is like "I can make this bike work. Just watch!"

And two, ease of adjust-ability, esp the ability to dial in the seat tilt accurately and be able to change the tilt and get it back exactly is, in my book, the mark of a good post. (To dial in at the start in the road with just a wrench and no measuring equipment is a huge help and being able to change the tilt say 1/3 of a bolt turn for a saddle sore, then a week later go back that 1/3 turn and have the tilt back exactly is just as or even bigger level of importance. The Thompson heasd is really nice in that respect. I have two mounted on 160 mm setback custom posts (and rails centered - life is good).

Ben