Important to remember, they won't draw the foundation unless there is a flow on. The bees will create the space they need, as they need it, but if there is nothing to store, they just "hang out" as you mentioned. The excluder is also an inhibiting factor for them. You can create the "flow" by feeding, but this time of year, it may be stored with the honey they have made, and adulterate it. Another thing to watch out for, is to suddenly find they have filled the brood nest with honey and completely ignored the foundation filled super. It pays to make an in depth inspection when things aren't moving along and we're learning "bee stuff". When bees are making honey, they spread nectar all over the place to cure, and can quickly tie up the brood nest with storage.
Recently, I looked in a main brood chamber and found it full of nectar. (there was a 3rd deep on them) The queen had been laying in the middle box. I was in a hurry, and closed the hive back up, planning on finding the queen and reversing the boxes on the weekend. When I went back in, they had moved most of the nectar out of the lower box into the 3rd deep and capped most of it. The queen was in the bottom box laying. Quite a suprise, but they did the manipulation I was planning on their own. I love it when a plan comes together.