In my snowy project snow tesselation is very important. I tried using both flat and PN tesselation and crack-free is checked.
But at 45* and lower angle of the camera, I have those pesky black triangles (much larger than tesselated poly, about the size of actual mesh triangle, I use mesh, not a landscape) at the bottom of a screen. There is consistent tesselation across all of the mesh with no distance falloff or anything tricky.
Tears your are getting are result of using adaptive tessellation, but not setting max displacement in material settings to appropriate value. It needs to be set to a maximum value ever you are going to supply to world displacement to calculate sufficient bounds and tessellate triangles offscreen.
