Originally Posted by
Turbotandem
Seat tube is 35mm. The XTR FD mounts are made in 2 clamp variety and 2 braze-on variety. I have the SM-FD 905H high mount which is only available in 34.9mm, with shims down to 31.8 and 28.6. So no, smaller seat tubes won't hold the FD closer to the frame centerline. Good thought though. It may be the low mount version or one of the braze-on mounted attachments may be more slim, but from the pictures online none appear slimmer.
Sounds like a product opportunity here... some people may want a "cammed shim" to adjust FD in/out position more than the limit screws allow. I'm not aware of any cammed shims in production.
Just FYW, Calfee's seattube spec is 34.9mm with either a removable shim or a fixed carbon wrap sleeve. Our Dragon build came with the fixed carbon (Di2 reinforcement) in the FD mount area, so no way to use an aftermarket shim.