Not very much air is needed. Try being a little more vigorous with your agitation, and/or extend the time you agitate. For example, if you are doing 5 seconds, try 10 seconds. Be consistent, and only make one change at a time.
Agitation seems to be a very personal thing, at least based on what I've seen in the threads with agitation questions. What works great for one person, works not at all for someone else, so the key is to introduce a reasoned change in your routine and test.