I've tried it all different ways. With the Nikon lens on 70mm and the Tamron 70-300mm set on 70mm The VC was still better than the VR, at least on my lenses. The VC held the image completely still, long enough to get a good picture. I still got a good picture with the Nikon too, but I saw more movement of the image in the viewfinder. My hands have gotten very shaky over the years. I don't know if it's nerves or the oncoming of Parkinsons. I suspect nerves, because of other things in day to day life. I also tried both lenses at 105mm, and same thing, The VC was better. But, I haven't noticed what you're talking about either. I've noticed no difference in the VR on the Nikon lens, whether it's at 18mm or 105mm. By the same token, I've noticed no difference with the Tamron, whether it's at 70mm or at 300mm. I will mess with it some more tomorrow, and pay even closer attention, and see what happens.
I had read that online before, and gave it a quick try, using those different settings. In the quick try (operative word being quick) the results were what's posted above. So, since you're real concerned about it, you've got me questioning my results. So, I'll try again, and really concentrate on it this time, trying to be more scientific about it. I'll post here what I find out...........