I am in a village that I have improved. I have fenced in the entire village and every building either has a staircase, glass block, or half slab for the length of the roof. However illagers are forming on top of half slabs. I cannot believe this is intentional, as you would essentially be making villages almost indefensable.  Which side note. We need 2 high fence gates if we are going to have mobs that easily fire ranged attacks at villagers over top of 1 high fences...

Including villages and raid data. Not sure if that will help.