You want to place your hub in the best category possible. But sometimes there is more than one category that a hub fits under. If you are not receiving traffic that is as good try putting it back in the other category and see what happens.
There are many things that affect a hub's traffic. If you feel it is in the best category try tweaking the title using the title turner or using the google keyword tool at https://adwords.google.com. Check your tags and make sure they are all relevant. These tell google what your hub is about and help describe it to search engines.