I noticed that that my saddle started moving down when riding (maybe 1cm/hour). When cleaning the inside of the seattube I noticed that the part at the height of the clamp became smooth, compared to the rest that has a texture designed to prevent the seat post from sliding down (see photo).
The seat clamp is a quick release one, installed by the shop. The height of the collar is 15mm.
Besides adding seatpost and seattube cleaning to the maintenance routine, and applying an "assembly paste", are there other techniques to increase the friction at this interface so that the seatpost remains in position?