One possible explanation:
From my observation, when the trees are leafed out (as they would have been in late summer), it's nearly impossible to tell that hill is there.
That's not a sufficient excuse for something so important, but I was struck by how difficult it was for me to gauge the elevations. On the other hand, I think the area was less wooded then, so perhaps that is even less of an excuse.
I was shocked when I looked at the topographical sheet and leaned that Nicodemus and what I think of as the Dunker Church plateau where S D Lee was set up are the same.