If you want to use 1d arrays for this style then to add the top segment I would create a second L1S generator, wire this to the same spline and using the same default input. You can then use the new generator's Properties > Z Offset
value to position to top bar.
You will notice that the top section overlaps the sides, to avoid this add a new empty segment to the start and end inputs and enter half the width of the sides into the left and right padding:
I've attached this solution in a file as well as a version with some exported parameters to demonstrate how the height can be easily parameterized and adjusted from the modify panel.
I hope that helps,