For these graphs, doesn't it imply there is an amount of distance between point A and B or a given takoff angle that define NVIS? This is very interesting as I built a separate 40 meter dipole and put it lower to the ground for the Wisconsin QSO party for in state contacts. It not an apples to apples comparison, but I'm finding in most cases my 40 meter dipole at 15-20ft is the same or better than a 176ft doublet from in state to about 2 states out. The doublet is ~30ft up. Sometimes I see up to 2 units better on the 40 meter dipole, but most often 1S unit in state and 2 states out. -kb0kfx