Thank you, this is great!
But there is just one thing - the spline should end where the wall ends, not where the coping ends. This is the part where I was struggling about the most.
This is important because when building the scenes I only have to consider the wall below, and the coping is just a decoration.
Also, I use the same spline to place fences, yet fences don't look great when they are right on the edge..
I draw a simple section to illustrate it.