So I put on a used (new to me) aliante on last night and noticed that the shape of the rails didn't match up with the shape of my seat post rail clamp (race face post).

It seems like the post clamp has a slightly different diameter than the rails. So instead of clamping all the way around the rail, it's only touching at 2 or 3 points. I think an easy (and extremely exaggerated) way to imagine what is happening is if you clamped a circle in a triangle shape.

Has anyone noticed a similar thing? Do different seat post rail clamps have different sizes?

this happened to my seat/rails as well. eventually when everything is tightened down the rails fit into place better.

Are they oval carbon rails?

I was thinking this too, but I'm scared to crank down on them too hard (they might collapse/snap or something). Even though they say it's Ti where you clamp down, I still worry.

They're carbon rails, with Ti in the clamping area. It's the Carbon Rail/Shell Aliante. I'll check tonight to see if they're oval or not.

Don't be afraid; when unscrewing my seat just yesterday to adjust the nose angle, i noticed the rails have adjusted themselves into place. this is <300mi