You should float at eye level. Some people float at forehead level or chin level, although eye level is most common. The important thing is that you're not sinking and not floating, but remaining steady.
If you don't remain steady at eye (or other part of the head) level and begin to sink you have too much weight - remove a unit of weight and restart the exercise from Step One. If you float, you don't have enough weight - add a unit of weight and restart the exercise from Step One.