If you have fitted a lightweight alloy seatpost clamp with a Ti bolt and a carbon fibre seatpost, you may find that even when done up tightly and with carbon paste, the post still slips.
You can tighten the bolt further but there is risk of either snapping the bolt, rounding off the hex head, stripping the thread in the clamp, or crushing the seatpost.
Having had this problem, looking at the clamp it is clear that as the clamp is tightened, the clamp ends are getting bent so the gap between then is not longer parallel. The force applied is bending the clamp instead of applying it to the seat tube and post.
To over come this, I have fitted a 0.5 mm washer in the gap so the ends of the clamp are no longer being bent and the force is bringing the ends nearest the seat tube together thus applying it to the seat tube. Obviously the thickness of the washer has to be chosen so that it does not prevent the clamp from being tightened.
(it also prevent the clamp from being over tightened)
The photo shows that the gap is almost parallel, there is a slight gap between the washer and the clamp nearest the seat tube - if the washer was not there, then ends furthest away from the seat tube would be would be almost touching.