I am about to purchase an IGS stand for my AF. I am going to get one with 2 lights per shelf but don't know if a 4-shelf unit will give me enough space between the plants and the lights or if I should go with a 3-shelf unit. I understand there are 17" between the lights and the shelf on the 4-shelf unit. Has anyone had experience with the IGS 4-shelf unit. Of course, I want to be able to fill it with as many plants as I can.