Here's a group of 9 tiles:

The discussion here relates to the heights of tile 5
My understanding is that from the "eaw16.hm" data the elevation of A is the value for tile 5, B is the value for tile 6, C is the value for tile 9, and D the value for tile 8.
The midpoint (M) illustrates VBH's "four triangle" approach.
So what is the height of M? I have not checked the code, but my guess is that it is the mean of A B C and D.
Looking at the possibility of a cliff face lets put A, B and D at 400 metres with C at sea level (0).
Based on my guess that would put M at 300 metres, with a 100 metre dip from A, B and D, and a 300 metre rise from the sea.
Given that the tile edge is 4.096 km and the diagonal approximately 5.6 km this illustrates the complexity of making an effective cliff face based entirely on tiles with the current constraints.

Jel