It seems to me that the "Areas of Focus" horizon doesn't really fit completely into the six Horizons model. Whereas the other horizons are specific outcomes that you intend to achieve, "Areas of focus" is more like a checklist of things you don't want to forget about. A grouping of outcomes, rather than an outcome itself. I can imagine having an Areas of Focus checklist for several of the horizons. For example, you could have Areas of focus above 40,000ft to ensure that you have imagined/visioned your future in all of the dimensions of your life - Health, Career, Finances, Relationships, etc. This applies, I believe, throughout the hierarchy.
In other words, in my mind a better structure would be to have 5 horizons - Actions, Projects, Objectives, Visions, Values - which define the outcomes you are committed to, and then an areas of focus checklist for each horizon that provides a grouping of outcomes to ensure that nothing is missed.
Am I insane?