I think the problem was that the feeder was in at the start and the bees made that the location for the cluster. I've put in jars in a new hive, but after they have established the location for the cluster. I would wait a day or so before putting in the sugar.
Normally the cluster will be at the front of the hive near the entrance, but in your case they clustered in the back. Like I said, I assume they did that to be close to the nectar.
What I would recommend in the future with a package is start with a dozen or so bars depending on the size of the hive. Once they get a cluster going and start making comb move the follower back and add the feed.
If you look at Wyatt Mangum's book (I think it was his) he puts the sugar right behind the brood nest. That may be a good idea, but if you miss an inspection and a flow hits you are in for a big mess. Putting it at the back of the hive gives you plenty of time to get it out.