On my world I built a teleporter going from 81 to 200 . The command inside of the command block is as follows: "/tp @a[r=3] -28 200 246". Whenever someone gets teleported by it, they're fine until they lower their current y coordinate. If you jump, increasing then decreasing your y coordinate, you die instantly. Same goes for lowering your y coordinate any other way. In other words, If you go down a block after teleporting to a different y coordinate you take fall damage corresponding to the differences in y from the sending and receiving teleportation coordinates.