Blending POM with common mapping

How can I blend POM layer with other or common, flat layer?
I’ve seen example of CG Spartans but there is a few visual bugs - layers are not blended, so when I changed height ratio I noticed differences between layers. That’s incorrect, because first layer can change coordinates faster than second layer.

I thought I would change a bit shader code (I have experience with games written using OpenGL) but it’s problematic to get access of landscape layer samples in specified coords.
Have You any idea how can I fix it?
I know that I should always use small values of height ratio, but it’s still not so good solution.