Change the seat post.I have a Thomson with mine and it works perfectly.
Two issues
1. I like my Brooks level or down in front (it's a brand new Swallow) I think that's personal taste
2. If using a Thomson post the front part where the bolt attaches sits up a little high and on mine and some others I've heard about, it contacts the underside of the saddle. I modified my Thomson post and it works perfectly so if you need me to show you pics or explain it let me know.