teleporting into a 2 block high space will cause suffocation damage, if you are floating/flying and teleport, you notice you aren't teleported onto the ground, you float above it, but if you change the coordinates from, lets say "0 59 0" to "0 58.9 0" you won't hit the ceiling, but you will fall trough the ground because it gets calculated as teleporting into the block

So: Teleporting into 2 block space teleports you too high = suffocation damage, teleporting lower will make you fall into the ground.