You shouldn't place glass on the first layer because when they blow it up they have to break 1 quick block to get your bed. It's best to place it in the middle of the defence
btw there is a formula to calculate how many blocks you need for a layer : 2 times X x X ( big X is the layer of beddefense and the bed is the first layer) so it woul be 2x2 x2 for the first layer you put on bed and 3x3 x2 for the second one
