Does your seatpost look like this (Kalloy SP248D from the 2014 Surly catalog Page 65)?

Amazon.com : Uno 248D Radiussed Top Seatpost 27.2 x 350mm Silver : Sports & Outdoors

It is adjustable, just loosen the bolt and move the saddle to the position you want and tighten it. Then hope it stays put.

I had the same seatpost on my LHT and had problems with the saddle moving backwards in the clamp and it wouldn't hold the angle. I replaced it with a two bolt model, Thomson Elite Setback. Not cheap but it does exactly what it is supposed to. If the seatpost at the Amazon link is the same one you have, the Thomson Setback model will put the saddle clamp at the same position.

https://www.bikethomson.com/product/elite-seatpost/

I also replaced the seatpost clamp with the Surly Constrictor (the seatpost was also slipping and fit loosly in the frame):

Small Parts | Parts and Accessories | Surly Bikes

You may want to get a second opinion on your bike fit.