…that's about average for a post that claims to have a setback. I believe my Thompson had something sucky like 18mm. I didn't like it really because the bend in the post limited the amount that the seat could go down. I have to say my LBS warned me about that aspect, but I wanted the sweet clamp and I didn't think it would be a problem but it turned out I was wrong.
The FSA seems to have a very nice clamp and a good amount of setback. I'm shopping for one of these myself, so post here if you find anything out.
Easton was recommended to me, but I'm looking for a post with a two-bolt clamp. There aren't that many designs out there that seem as sweet as the Thompson and the FSA clamps. Don't overlook Salsa. They have a good post with setback as well.