Gates and/or build fire pits into the walls?

See I tried building fire pits into the walls and I got nothing, it was still being blocked by the walls next to it, it's almost like the same thing when building them in tree'd areas, if there is a tree cell blocking it's left and right, the domain won't go forward through the route in front of it, you have to break a tree to free up a walk space for the domain to expand forward. So walls don't work. I haven't tinkered with too many gates but I do know that once you put up walls in front to make a maze, it blocks the domain again at a certain point.