I think the rails are designed that way..I no when I put my saddle on a flat surface, it tilts downward. I can rotate my seat up and down on my seat post though, so the farther back I put my seat, the more I have to rotate my seat up..It seems like most seat posts have this function, I don't know about Ultegra off the top of my head though.

The Thompson seat post is highly regarded. I may swap out my carbon seat post for one.