Dubbya, I have read and followed your posts on this subject and realize how diligent you are in researching and testing this so I can forgo the usual warnings and links to the Lens Rental articles.
But honestly, I think this is more serendipitous and you can't necessarily draw any conclusive conclusion from it.
In my experience with testing, I found that short focal lengths tended to have more AF variation than longer focal lengths.
And out of the six lenses in my profile (3 FX and 3 DX) I am satisfied with all but two; the Nikkor 18-105 and Sigma 50-150 (both DX lenses). With those two I feel that in most circumstances I achieve better AF accuracy with AF Fine Tuning.