I'm using a Brooks Swift on a Nitto Crystal Fellow seatpost, and I'm having ongoing problems with the clamp of the seatpost gradually slipping backwards on the post, lifting the nose of the saddle upwards as it goes. (The rails are secure in the clamp, it's just the clamp that's moving.) I have the saddle all the way back, which I'm sure makes it worse, but I'm not all that heavy of a rider (170#), FWIW.

Any suggestions as to how to avoid this? Roughen up the mating surfaces with a bit of sandpaper? Get a longer Allen wrench and torque the bolt more? Something else?