In my Minecraft world, I have an enderman XP farm, which I (obviously) use to fix my weapons, tools and armor. It's my model (no tutorial used), and it works just fine... except the fact that endermen teleport to the top because of fall damage. This gets very annoying after a while (mainly because it reaches the mob cap faster).
To try to fix this, I have placed slabs (seen in the screenshot) to try to prevent them from teleporting. The only thing that it does is make my farm go faster (which I really like), but they still teleport anyway.
So, the question I have is: How can I prevent endermen from teleporting at the top of my XP farm?