The basic rules are keep the bed 2 away from anywhere mobiles can get. I think for vertical distances the distance needs to be a little further away.. As it stands right now though in 1.5 there is a bug where beds are not always safe, even if they should be. Could be as simple as moving it to a different wall/location within the room above.. Also make sure there you are enclosed and well lit.. It is hard to tell but it would almost look like something could spawn where you are standing to take the second screen shot (The spawn range rules do not apply when sleeping it seems).
