The sill and range do not refer to any particular elevation value (in fact, they apply to all elevation values). These numbers tell you the distance at which two points are no longer correlated (the range), and the expected squared difference in their elevation values (sill). The semivariogram plots the squared difference in elevation between pairs of points that are a given distance apart. It only operates on the difference in elevation values, not on the actual elevation value.
For example, imagine two points that are 2000 meters apart. One has an elevation of 1000 meters, and the other has an elevation of 1100 meters. The squared difference in elevation value is 100^2=10000, so this pair would get plotted at (2000, 10000) in the semivariogram.
Now, imagine another pair of points that are also 2000 meters apart, but their elevation values are 100 meters and 200 meters. Their squared difference in elevation is also 10000, so this pair would also be plotted at (2000, 10000) in the semivariogram.
Hopefully you can see that you cannot extract an elevation value where the the semivariogram reaches the sill because semivariograms are not constructed to answer that kind of question.
