Currently walls are either not built, or all wall entities in the blueprint are placed every time a new piece of track is placed. This means that you can't build wall patterns wider than 2 tiles automatically with FARL, because if you try they will overlap, like in this video: https://www.youtube.com/watch?v=kEF4FwF4Epw

Since biters can be quite powerful in the late game - or earlier in modded games - , it's useful to have wall designs that instead of blocking the enemies aim to slow them down, because otherwise they would get destroyed pretty quickly. I, in the video linked above, am trying to use a 6 tile wide wall design, but can't do that because the placing of walls are forced to work in a different way

My suggestion would be to build the walls included in the blueprint besides the previously built one