An interesting question… there is also the possibility of directly adjusting position/tension like this
Or I’ve also been considering an option with inclined planes. Let’s see if I can describe…
This configuration could have a slot (only allowing 1-2 mm perhaps of travel) in the green part, and a circular hole in the red/brown part, and tightening the nut/bolt axially squeezes the red parts and also forces it toward the rail. More complex and easy to over-tighten. Probably not workable but in the spirit of brainstorming perhaps it will inspire a better idea.