You can use the Clipping Area > Expand
value to enlarge the area before clipping. Increase the value until the ceiling is centred horizontally.
Once you have the ceiling centered, to adjust it vertically add an empty segment to the bottom input. Open the segment's properties and enter a value in the Left
and Right Padding
. It doesn't really matter what this is, RailClone ignores segments with no size on the x axis so this prevents that.
You can then control the offset vertically by adjusting the Segment's Y Fixed Size
In the attached file I've exported these two properties to make them easier to access. I hope that helps, please let me know if I can help further.