Not sure how acurate this info is, but it's worth a post.
Check inside the frames seat tube to determine if there's an aluminum sleeve present. If there is, it should be 4 inches long.
Because certain carbon frames seat tubes flex while riding, you have to be sure the seatpost does not extend very far past the bottom of the sleeve. Otherwise, the bottom edge of the seat post MAY rub against the carbon seat tube if the seatpost is set really deep into the frames seat tube.
Does that make sense?
I'm guessing the info applies to really long 400mm seatposts.
The velo orange seatpost is the same length as the stock. The Frame has the al clamp. Kinda glad I tried this out as I found a crack in the OEM post. I have a torque wrench and it has never been tightened above the recomended 9 Nm force. I'm ordering Park SuperGrip and another Velo Orange seatpost to replace the OEM post. I'm a Clyde (230 lbs) so this doesn't surprise me.